Invalidate CloudFlare cache on updates

The playbook is still served by CloudFlare so everytime something
changes we need to invalidate the nebulab.com cache.

.github/workflows/cache.yml

@@ -0,0 +1,20 @@
+name: clear-cache
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Wait for CloudFlare pages to finish the deploy
+        uses: jakejarvis/[email protected]
+        with:
+          time: '6m'
+      - name: Purge CloudFlare Cache
+        uses: jakejarvis/[email protected]
+        env:
+          CLOUDFLARE_ZONE: ${{ secrets.CLOUDFLARE_ZONE }}
+          CLOUDFLARE_TOKEN: ${{ secrets.CLOUDFLARE_TOKEN }}