docs: add documentation

plugins/github-actions/README.md

@@ -1,13 +1,70 @@
-# github-actions
+# GitHub Actions Plugin
 
-Welcome to the github-actions plugin!
+Website: [https://github.com/actions](https://github.com/actions)
 
-_This plugin was created through the Backstage CLI_
+## Screenshots
 
-## Getting started
+TBD
 
-Your plugin has been added to the example app in this repository, meaning you'll be able to access it by running `yarn start` in the root directory, and then navigating to [/github-actions](http://localhost:3000/github-actions).
+## Setup
+### Generic Requirements
+1. Provide OAuth credentials:
+    1. [Create an OAuth App](https://developer.github.com/apps/building-oauth-apps/creating-an-oauth-app/) with callback URL set to ```https://localhost:3000/auth/github```.
+    2. Take Client ID and Client Secret from the newly created app's settings page and put them into ```AUTH_GITHUB_CLIENT_ID``` and ```AUTH_GITHUB_CLIENT_SECRET``` env variables.
+2. Annotate your component with a correct GitHub Actions repository and owner:
+    
+    The annotation key is ```backstage.io/github-actions-id```.
 
-You can also serve the plugin in isolation by running `yarn start` in the plugin directory.
-This method of serving the plugin provides quicker iteration speed and a faster startup and hot reloads.
-It is only meant for local development, and the setup for it can be found inside the [/dev](/dev) directory.
+    Example:
+    ```
+    apiVersion: backstage.io/v1alpha1
+    kind: Component
+    metadata:
+      name: backstage
+      description: backstage.io
+      annotations:
+        backstage.io/github-actions-id: 'spotify/backstage'
+    spec:
+      type: website
+      lifecycle: production
+      owner: guest
+      ```
+### Standalone app requirements
+If you didn't clone this repo you have to do some extra work.
+
+1. Add plugin API to your Backstage instance:
+
+```bash
+yarn add @backstage/plugin-github-actions
+```
+
+```js
+// packages/app/src/api.ts
+import { ApiRegistry } from '@backstage/core';
+import { GithubActionsClient, githubActionsApiRef } from '@backstage/plugin-github-actions';
+
+const builder = ApiRegistry.builder();
+builder.add(githubActionsApiRef, new GithubActionsClient());
+
+export default builder.build() as ApiHolder;
+```
+
+2. Add plugin itself:
+
+```js
+// packages/app/src/plugins.ts
+export { plugin as GithubActions } from '@backstage/plugin-github-actions';
+```
+
+3. Run the app with `yarn start` and the backend with `yarn --cwd packages/backend start`, navigate to `/github-actions/`.
+
+## Features
+
+- List workflow runs for a project
+- Dive into one run to see a job steps
+- Retry runs
+- Pagination for runs
+
+## Limitations
+
+- There is a limit of 100 apps for one OAuth client/token pair