add cron action to auto-fetch new mentions from webmention.io

[skip ci]

.github/workflows/webmentions.yml

@@ -0,0 +1,26 @@
+name: Fetch Webmentions
+
+on:
+  schedule:
+  - cron: '0 */3 * * *'   # run every three hours at top of hour
+
+jobs:
+  fetch:
+    runs-on: ubuntu-latest
+    env:
+      WEBMENTIONS_TOKEN: ${{ secrets.WEBMENTIONS_TOKEN }}
+      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 1
+        lfs: false
+    - name: Get webmentions data
+      run: |
+        wget -nv -O data/webmentions.json "https://webmention.io/api/mentions.json?domain=jarv.is&token=$WEBMENTIONS_TOKEN"
+    - name: Push changes
+      run: |
+        git config --global user.name "github-actions[bot]"
+        git config --global user.email "41898282+github-actions[bot]@users.noreply.github.com"
+        git commit -am "Add new webmentions 🎉" -m "[skip ci]" || echo "No new mentions... 😢"
+        git push origin main