Add composite github action

README.md

@@ -6,4 +6,28 @@ Program to simplify PCI double approval process across repositories
 
 0. Install nix
 1. Run `nix-shell`
-2. Run `cargo run`
+2. Run `cargo build`
+3. Run `cargo test`
+4. Run `cargo deny check`
+
+## GitHub Action usage
+
+pear-reviewer can be used as a GitHub Actions workflow to comment the review template on PRs.
+
+```yaml
+name: pear-reviewer
+on:
+  pull_request:
+    branches:
+      - '*'
+
+permissions:
+  pull-requests: write
+
+jobs:
+  review:
+    name: Review
+    runs-on: ubuntu-latest
+    steps:
+      - uses: sapcc/pear-reviewer@main
+```

action.yaml

@@ -0,0 +1,42 @@
+name: 'pear-reviewer'
+description: 'Run pear-reviewer'
+runs:
+  using: "composite"
+  steps:
+    - name: Check out code
+      uses: actions/checkout@v4
+
+    - name: Run pear-reviewer
+      id: run-pear-reviewer
+      uses: docker://ghcr.io/sapcc/pear-reviewer:latest
+      run:
+        pear-reviewer > $GITHUB_OUTPUT
+
+    - name: Find Comment
+      uses: peter-evans/find-comment@v3
+      id: find-comment
+      with:
+        issue-number: ${{ github.event.pull_request.number }}
+        comment-author: 'github-actions[bot]'
+        body-includes: <!-- written by pear-reviewer -->
+
+    - name: Create comment
+      if: steps.find-comment.outputs.comment-id == ''
+      uses: peter-evans/create-or-update-comment@v4
+      with:
+        issue-number: ${{ github.event.pull_request.number }}
+        body: |
+            <!-- written by pear-reviewer -->
+
+            ${{ steps.run-pear-rewiwer.outputs.comment }}
+
+    - name: Update comment
+      if: steps.find-comment.outputs.comment-id != ''
+      uses: peter-evans/create-or-update-comment@v4
+      with:
+        comment-id: ${{ steps.find-comment.outputs.comment-id }}
+        body: |
+            <!-- written by pear-reviewer -->
+
+            ${{ steps.run-pear-rewiwer.outputs.result }}
+        edit-mode: replace