ci: pr add label

.github/workflows/pr-branch.yml

@@ -0,0 +1,16 @@
+name: Add Label
+
+on: [ pull_request ]
+
+env:
+  BASE_BRANCH: ${{ github.base_ref }}
+
+jobs:
+  add_label:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-ecosystem/action-add-labels@v1
+        if: ${{ startsWith(github.event.comment.body, '/add-labels') }}
+        with:
+          labels: env.BASE_BRANCH