add autoupdate workflow

.github/workflows/autoupdate.yml

@@ -0,0 +1,25 @@
+name: autoupdate
+
+on:
+  schedule:
+    - cron:  '0 0 * * 6'
+
+jobs:
+  merge-upstream:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+    - name: Add upstream repo
+      run: git remote add upstream https://github.com/TryGhost/Casper.git
+    - name: Checkout master
+      run: git checkout master
+    - name: Merge upstream
+      run: git pull upstream main
+    - name: Push changes
+      uses: ad-m/github-push-action@master
+      with:
+        github_token: ${{ secrets.GITHUB_TOKEN }}
+        branch: ${{ github.ref }}
+        tags: true