Improve documentation and add contributing guide

CONTRIBUTING.md

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+# Contributing to d2-additional-info
+
+Thank you for your interest in contributing!
+
+## Table of Contents
+
+- [Getting Started](#getting-started)
+- [Development Workflow](#development-workflow)
+- [Code Style](#code-style)
+- [Project Structure](#project-structure)
+- [Adding New Generators](#adding-new-generators)
+- [Testing Your Changes](#testing-your-changes)
+- [Commit Guidelines](#commit-guidelines)
+- [Pull Request Process](#pull-request-process)
+- [Common Tasks](#common-tasks)
+
+## Getting Started
+
+### Prerequisites
+
+- **Node.js** >= 22 ([Download](https://nodejs.org/))
+- **pnpm** >= 10 ([Installation](https://pnpm.io/installation))
+
+### Initial Setup
+
+1. Fork and clone the repository
+2. Run `pnpm install`
+3. Run `pnpm generate-data` to verify setup
+
+## Development Workflow
+
+### Making Changes
+
+1. Create a new branch
+2. Make your changes
+3. Test your changes (see [Testing Your Changes](#testing-your-changes))
+4. Run `pnpm fix:eslint`
+5. Commit and push to your fork (Prettier runs automatically on commit)
+6. Open a Pull Request
+
+## Code Style
+
+This project uses:
+- **ESLint 9** with flat config for linting
+- **Prettier** for code formatting
+- **Husky** for pre-commit hooks
+
+### Pre-commit Hooks
+
+Prettier automatically formats staged files and organizes imports when you commit.
+
+### Style Guidelines
+
+- Use TypeScript for all new code
+- Follow existing code patterns in similar scripts
+- Use descriptive variable names
+- Add comments for complex logic
+- Use the `writeFile()` helper from `helpers.ts` for file output
+- Use `@d2api/manifest-node` for Destiny 2 manifest access
+
+## Project Structure
+
+```
+d2-additional-info/
+├── src/                          # TypeScript source files
+│   ├── generate-*.ts            # Data generation scripts
+│   ├── main.ts                  # Orchestrates script execution
+│   ├── helpers.ts               # Shared utility functions
+│   └── log.ts                   # Logging utilities
+├── output/                       # Generated JSON/TypeScript files
+├── data/                         # Static data and config files
+│   ├── events/                  # Event-related data
+│   ├── seasons/                 # Season-related data
+│   └── generated-enums.ts       # Auto-generated enums
+├── built/                        # Compiled JavaScript
+└── .husky/                       # Git hooks
+```
+
+### Key Files
+
+- **`src/main.ts`** - Entry point that runs all generator scripts in order
+- **`src/helpers.ts`** - Shared utilities like `writeFile()` and `readJsonFile()`
+- **`src/generate-*.ts`** - Individual generator scripts (one per output file)
+
+### Script Execution Order
+
+Generator scripts run in this order:
+1. **Priority scripts** (in exact order):
+   - `enums` - Generates TypeScript enums from manifest
+   - `season-info` - Generates season data
+   - `source-info` - Generates source mappings
+   - `watermark-info` - Generates watermark mappings
+   - `universal-ornament-plugsethashes` - Generates ornament plug set hashes
+2. **All other scripts** run alphabetically
+
+Priority scripts generate data that other scripts depend on.
+
+## Adding New Generators
+
+To create a new data generator:
+
+1. **Create a new file** in `src/` named `generate-your-feature.ts`
+
+2. **Follow this pattern**:
+   ```typescript
+   import { getAllDefs, getDef } from '@d2api/manifest-node';
+   import { writeFile } from './helpers.js';
+
+   const TAG = 'YOUR-FEATURE';
+
+   // Fetch data from manifest
+   const items = getAllDefs('InventoryItem');
+
+   // Process data
+   const result: Record<number, string> = {};
+   items.forEach((item) => {
+     // Your logic here
+     result[item.hash] = item.displayProperties.name;
+   });
+
+   // Write output file
+   writeFile('./output/your-feature.json', result);
+   ```
+
+3. **If other scripts will depend on your script's output**, add your script to `prioritizedScripts` in `src/main.ts` to ensure it runs first
+
+4. **Document your output file** in README.md's "Output Files" section
+
+5. **Test your generator**:
+   ```bash
+   pnpm generate-data-sub your-feature
+   ```
+
+### Important: Module Caching
+
+If your script reads a JSON file that's written by another script during the same `generate-data` run, use `readJsonFile()` instead of static imports:
+
+```typescript
+// ❌ Don't use static imports for files written during the same run
+import seasons from 'data/seasons/seasons_unfiltered.json' with { type: 'json' };
+
+// ✅ Use readJsonFile to bypass Node.js module cache
+import { readJsonFile } from './helpers.js';
+const seasons = readJsonFile<Record<string, number>>('./data/seasons/seasons_unfiltered.json');
+```
+
+This ensures you always read the latest data from disk, not cached data from before the current run.
+
+## Testing Your Changes
+
+### Test Individual Scripts
+
+```bash
+pnpm generate-data-sub script-name
+```
+
+Where `script-name` is the generator filename without the `generate-` prefix and `.ts` extension. For example, `src/generate-season-info.ts` → `season-info`.
+
+Example:
+```bash
+pnpm generate-data-sub season-info source-info
+```
+
+### Test All Scripts
+
+```bash
+pnpm generate-data
+```
+
+### Verify Output
+
+1. Check that your output file appears in `output/`
+2. Verify the file contains expected data
+3. Ensure no errors were logged during generation
+4. Check for unexpected changes in other output files
+
+> **⚠️ Important:** NEVER manually edit JSON files anywhere (including `output/` or `data/`). All JSON files are generated by scripts and manual edits will be overwritten. If output is incorrect, fix the generator script or update TypeScript config files in `data/`, then re-run generators.
+
+## Commit Guidelines
+
+Write clear commit messages that describe what changed and why. No strict format required.
+
+## Pull Request Process
+
+### Before Submitting
+
+- Run `pnpm lint:eslint`
+- Run `pnpm generate-data`
+- Update README.md if you added new output files
+
+### PR Description
+
+Include:
+- What you changed and why
+- How to test the change
+- Link to related issues (if any)
+
+## Common Tasks
+
+> **⚠️ Golden Rule:** Never manually edit JSON files or `data/generated-enums.ts`. All JSON files (in `output/` or `data/`) are generated by scripts. You CAN edit TypeScript config files in `data/` (e.g., `bounty-config.ts`). If JSON data is wrong, fix the generator script or update TypeScript config files, then re-run the generators.
+
+### Manifest Updates
+
+Manifest updates are handled automatically by GitHub Actions. You don't need to do anything.
+
+### Add Missing Items or Update Configuration
+
+1. Check for a TypeScript config file in `data/` (e.g., `bounty-config.ts`)
+2. Update the config file or generator script (NOT JSON files!)
+3. Run the generator to regenerate output
+4. Submit a PR with the updated config/script and regenerated output
+
+## Questions?
+
+- **Join the DIM Discord** for quick help and discussion
+- **Check existing issues** on GitHub
+- **Ask in a new issue** if you need help
+- **Look at existing generators** for examples
+
+## Code of Conduct
+
+Be respectful and constructive in all interactions.
+
+---
+
+Thank you for contributing to d2-additional-info!