Added intro, examples and contributions to readme

Author: pkpio

README.md

@@ -1,3 +1,33 @@
+# Introduction
+
+This repository contains an [Azure DevOps Task](https://docs.microsoft.com/en-us/azure/devops/pipelines/process/tasks?view=azure-devops&tabs=yaml) and a [GitHub Workflow Action](https://help.github.com/en/actions/automating-your-workflow-with-github-actions/workflow-syntax-for-github-actions#jobsjob_idsteps). See below usage examples to start using this in your CI. 
+
+This is currently in very early stages so, features offered are very limited. See [contributing section](#contributing) below if you would like to chip in some features. At this stage, this repo is more of a skeleton upon which we hope to add more functionality. Once this is in a good state, we can be on top of our app size changes and very likely make this repo public.
+
+## Usage examples
+
+- In a Azure DevOps Pipeline
+
+   ```yml
+    - task: android-app-size-diff-task@0
+      inputs:
+        baseAppPath: test/assets/test.apk
+        targetAppPath: test/assets/test.apk
+        summaryOutputPath: summary.md
+      displayName: Run APK size comparision
+   ```
+   
+- In a GitHub Workflow (only after this repo becomes public)
+
+   ```yml
+     - uses: microsoft/android-app-size-ci@v1
+       name: Run APK size comparision
+       with:
+        baseAppPath: test/assets/test.apk
+        targetAppPath: test/assets/test.apk
+        summaryOutputPath: summary.md
+   ```
+
 
 # Contributing
 
@@ -12,3 +42,37 @@ provided by the bot. You will only need to do this once across all repos using o
 This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/).
 For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or
 contact [[email protected]](mailto:[email protected]) with any additional questions or comments.
+
+## Setting up development
+
+Starting by cloning the repository. If your changes are small, feel free to open a PR with changes and the CI will take care of testing that everything still works with your changes. For something more long term or local testing, read on.
+
+When contributing, please be aware that **this repo will go public eventually**
+
+### Installations
+- Install all global dependencies
+  ```shell
+  npm install -g typescript
+  npm install -g ts-node
+  npm install -g mocha
+  
+  # Only if you are compiling the GitHub plugin
+  npm install -g @zeit/ncc
+  
+  # Only if you are publishing to ADO. Not required for most scenarios
+  npm install -g tfx-cli
+  ```
+- Install all project dependencies
+  `npm install`   
+  
+### Running 
+
+See `package.json` for full list of npm tasks. The below should be sufficient to get you started
+
+- Build code `npm run build`
+- Run ADO plugin locally `npm run adoTask`
+  - See [ADO Custom Task docs](https://docs.microsoft.com/en-us/azure/devops/extend/develop/add-build-task?view=azure-devops#run-the-task) to understand what variables to set - basically all task inputs
+- Run all tests `npm run test`
+  - Likely a better way to test your changes
+- Bundle all plugins `npm run bundle`
+