Adds docs

Author: orta

README.md

@@ -1,22 +1,57 @@
-A GitHub action that lets code-owners merge code via GitHub reviews.
+A GitHub action that lets code-owners merge PRs via a comment.
+
+This action uses the standardized structure of [a CODEOWNERS file](https://github.blog/2017-07-06-introducing-code-owners/) to handle the access controls. 
+
+## A simple example
+
+So, with this file at: `.github/CODEOWNERS`:
+
+```sh
+README.md @orta
+```
+
+If a PR contained _only_ a change to the `README.md` - this action would say that "@orta has the ability to merge by commenting 'LGTM'".
+
+Then, when/if this happens the GitHub Action will merge for you.
+
+## A real-world example
+
+`.github/CODEOWNERS`:
+
+```sh
+# Collaborators for Japanese Translation of the Website
+packages/playground-examples/copy/ja/** @sasurau4 @Quramy @Naturalclar @Takepepe @orta
+packages/tsconfig-reference/copy/ja/** @sasurau4 @Quramy @Naturalclar @Takepepe @orta
+packages/typescriptlang-org/src/copy/ja/** @sasurau4 @Quramy @Naturalclar @Takepepe @orta
+packages/documentation/copy/ja/** @sasurau4 @Quramy @Naturalclar @Takepepe @orta
+```
+
+This allows any of `@sasurau4`, `@Quramy`,  `@Naturalclar`, `@Takepepe` or `@orta` to merge PRs which affect their areas of the translation process in the TypeScript Website repo.
+
+## Setting It Up
+
+You want a unique workflow file, e.g. `.github/workflows/codeowners-merge.yml`
 
 ```yml
-name: Example Workflow
+name: Codeowners merging
 on:
   pull_request_target:
   issue_comment: { types: created }
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
-    
+
     steps:
     - uses: actions/checkout@v1
-    - name: Runs this workflow
+    - name: Run Codeowners merge check
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       uses:  orta/code-organizer-merge-on-green@master
+```
 
+Then you should be good to go.
 
-```
+### Security
+
+We force the use of [`pull_request_target`](https://github.blog/2020-08-03-github-actions-improvements-for-fork-and-pull-request-workflows/) as a workflow event to ensure that someone cannot change the CODEOWNER files at the same time as having that change be used to validate if they can merge.