add auto rebase action workflow (#35)

* add auto rebase action workflow

* use full sha

* Update auto-update.yml

Author: dasormeter

.github/workflows/auto-update.yml

@@ -0,0 +1,14 @@
+name: Auto-update
+# Auto-update only listens to `push` events.
+# If a pull request is already outdated when enabling auto-merge, manually click on the "Update branch" button a first time to avoid having to wait for another commit to land on the base branch for the pull request to be updated.
+on: push
+
+jobs:
+  Auto:
+    name: Auto-update
+    runs-on: ubuntu-latest
+    steps:
+      - uses: tibdex/auto-update@4081c5bdc34560b58288a010318054e63e6f4a51
+        with:
+          github_token: ${{ secrets.AUTO_REBASE_PAT }}
+