doc(README): add description how to use the action (#2) (#22)

Author: AndreasAugustin

README.md

@@ -1,10 +1,50 @@
-# template
+# actions-template-sync
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 ![Lint](https://github.com/AndreasAugustin/actions-template-sync/workflows/Lint/badge.svg)
 
+It is possible to create repositories within Github with
+[GitHub templates](https://docs.github.com/en/github/creating-cloning-and-archiving-repositories/creating-a-template-repository).
+This is a nice approach to have some boilerplate within your repository.
+Over the time the template repository will get some code changes.
+The problem is that the already created repositories won't know about those changes.
+This GitHub action will help you to keep track of the template changes.
+
+## Features
+
+* Sync template repository with the current repository
+
+## Usage
+
+### GitHub Actions
+
+Add this configuration to your github action
+
+```yaml
+# File: .github/workflows/template-sync.yml
+
+on:
+  schedule:
+  - cron:  "*/15 * * * *"
+jobs:
+  repo-sync:
+    runs-on: ubuntu-latest
+
+    steps:
+      # To use this repository's private action, you must check out the repository
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: actions-template-sync
+        uses: actions/actions-template-sync
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          source_repo_path: <the_path_to_the_repo>
+```
+
+You will receive a pull request within your repository if there are some changes available.
+
 ## DEV
 
 The development environment targets are located in the [Makefile](Makefile)