docs(setup): Add installation and usage instructions

Author: Ray Schamp

README.md

@@ -1,6 +1,59 @@
 # Scratch ESLint config
 #### eslint-config-scratch defines the eslint rules used for Scratch Javascript projects
 
+## Installation
+Install the config along with its peer dependencies, eslint and babel-eslint.
+```bash
+npm install -D eslint-config-scratch eslint@3 babel-eslint@7
+```
+
+If you're using the React config, also install the dependency for that
+```bash
+npm install -D eslint-plugin-react@6
+```
+
+## Usage
+The configuration is split up into several modules:
+* `scratch`: The base configuration. Always extend this.
+* `scratch/node`: Rules for node, e.g., server-side code, tests, and scripts
+* `scratch/es6`: Rules for ES6, for use when you're transpiling with webpack
+* `scratch/react`: Rules for React projects
+
+Usually web projects have a mix of node and web environment files. To lint both
+with the appropriate rules, set up a base `.eslintrc.js` with the rules for node
+and then override the node configuration in `src` (where web code usually lives).
+E.g., with a file structure like this:
+```
+scratch-project
+- .eslintrc.js
+- package.json
+- src
+  - .eslintrc.js
+  - index.js
+```
+Your config files should be set up like
+```javascript
+// scratch-project/.eslintrc.js
+module.exports = {
+    extends: ['scratch', 'scratch/node'],
+    env: {
+        node: true
+    }
+};
+
+// scratch-project/src/.eslintrc.js
+module.exports = {
+    root: true,
+    extends: ['scratch', 'scratch/es6', 'scratch/react'],
+    env: {
+        browser: true
+    }
+};
+```
+This will set up all the files in the project for linting as Node.js by default,
+except for those in `src/`, which will be linted as ES6 and React files.
+
+
 ## Committing
 This project uses [semantic release](https://github.com/semantic-release/semantic-release)
 to ensure version bumps follow semver so that projects using the config don't
@@ -23,5 +76,6 @@ Now you're ready to make commits using `git cz`.
 ## Breaking changes
 If you're committing a change that makes the linter more strict, or will
 otherwise require changes to existing code, ensure your commit specifies a
-breaking change.  This will cause a major version bump so downstream projects
-must choose to upgrade the config and will not break the build unexpectedly.
+breaking change.  In your commit body, prefix the changes with "BREAKING CHANGE: "
+This will cause a major version bump so downstream projects must choose to upgrade
+the config and will not break the build unexpectedly.

package.json

@@ -26,7 +26,7 @@
     "scratch"
   ],
   "optionalDependencies": {
-    "eslint-plugin-react": "^6.4.1"
+    "eslint-plugin-react": "6.x"
   },
   "peerDependencies": {
     "babel-eslint": "7.x",