Sync README to gh-pages

- updated README to use absolute URLs
- add workflow to sync README.md on changes to gh-pages branch

Taken from prometheus-community/helm-charts#41

Signed-off-by: Torsten Walter <mail@torstenwalter.de>

.github/workflows/sync-readme.yaml

@@ -0,0 +1,23 @@
+on:
+  push:
+    branches:
+      - 'main'
+    paths:
+      - 'README.md'
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - run: |
+          cp -f README.md ${{ runner.temp }}/README.md
+      - uses: actions/checkout@v2
+        with:
+          ref: gh-pages
+      - run: |
+          cp -f ${{ runner.temp }}/README.md .
+          git config user.name "$GITHUB_ACTOR"
+          git config user.email "$GITHUB_ACTOR@users.noreply.github.com"
+          git add README.md
+          git commit --signoff -m "Sync README from main"
+          git push

README.md

@@ -17,12 +17,15 @@ helm repo add jenkinsci https://charts.jenkins.io
 
 You can then run `helm search repo jenkinsci` to see the charts.
 
-Chart documentation is available in [jenkins directory](./charts/jenkins/README.md).
+<!-- Keep full URL links to repo files because this README syncs from main to gh-pages.  -->
+Chart documentation is available in [jenkins directory](https://github.com/jenkinsci/helm-charts/blob/main/charts/jenkins/README.md).
 
 ## Contributing
 
-We'd love to have you contribute! Please refer to our [contribution guidelines](CONTRIBUTING.md) for details.
+<!-- Keep full URL links to repo files because this README syncs from main to gh-pages.  -->
+We'd love to have you contribute! Please refer to our [contribution guidelines](https://github.com/jenkinsci/helm-charts/blob/main/CONTRIBUTING.md) for details.
 
 ## License
 
-[Apache 2.0 License](./LICENSE).
+<!-- Keep full URL links to repo files because this README syncs from main to gh-pages.  -->
+[Apache 2.0 License](https://github.com/jenkinsci/helm-charts/blob/main/LICENSE).