ci: add comment-on-pr.yaml (#1281)

* Create comment-on-pr.yaml

* Update .github/workflows/comment-on-pr.yaml

.github/workflows/comment-on-pr.yaml

@@ -0,0 +1,25 @@
+name: comment-on-pr
+
+on:
+  pull_request:
+    types:
+      - opened
+    branches:
+      - beta/v0.[0-9]+.[1-9]+
+
+jobs:
+  comment:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Create comments
+        run: |
+          cat << EOF > comments
+          ### Merging guidelines for the beta branch
+          Please use `Squash and merge` as the default.
+          However, when incorporating multiple changes with cherry-pick, use a `Create a merge commit` to preserve the changes in the history.
+          EOF
+      - name: Post comments
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          URL: ${{ github.event.pull_request.html_url }}
+        run: gh pr comment -F ./comments "${URL}"