Add a README for set-imgpkg-bundle-as-vendir-path

Author: lnhrdt

set-imgpkg-bundle-as-vendir-path/README.md

@@ -0,0 +1,54 @@
+# set-imgpkg-bundle-as-vendir-path GitHub Action
+
+The **set-imgpkg-bundle-as-vendir-path** action sets an [imgpkg](https://carvel.dev/imgpkg/) bundle image as a [vendir](https://carvel.dev/vendir/) path. This is useful for managing environment promotion and release management via GitOps.
+
+## Usage
+
+This action sets a directory under the top-level `channels` directory in `vendir.yml` to a specified imgpkg bundle image. If `vendir.yml` does not exist, it will be created. The action ensures that the `channels` directory is always the first top-level directory in `vendir.yml` so that other configurations can reference it as needed.
+
+Given a vendir.yml structured like this:
+
+```yaml
+# vendir.yml
+apiVersion: vendir.k14s.io/v1alpha1
+kind: Config
+directories:
+  - path: channels
+    contents:
+      - path: latest
+        imgpkgBundle:
+          image: registry.example.com/repository/bundle:build-1
+  - path: environments
+    contents:
+      - path: development
+        directory:
+          path: channels/latest
+```
+
+The following job will update the `imgpkgBundle` for channels/latest to use the `build-2` tag:
+
+```yaml
+jobs:
+  update-vendir:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Update latest release channel
+        uses: codebandits/github-actions/set-imgpkg-bundle-as-vendir-path@main
+        with:
+          channel_name: latest
+          imgpkg_bundle_image: registry.example.com/repository/bundle:build-2
+          bearer_token: ${{ secrets.SOME_BEARER_TOKEN }}
+```
+
+## Inputs
+
+- `channel_name`: **Required**. The path under the channels directory in vendir.yml to update.
+- `imgpkg_bundle_image`: **Required**. The published imgpkg bundle image.
+- `bearer_token`: Optional. The bearer token for authentication with the registry. Defaults to empty (no authentication).
+- `path`: Optional. The base directory path where vendir.yml is located. Defaults to `.` (current directory).
+
+## Outputs
+
+This action does not define any outputs.