ci: ask users to provide towncrier snippet

.github/workflows/towncrier.yml

@@ -0,0 +1,16 @@
+---
+name: Check PR change log
+
+on:
+  pull_request:
+    types: [opened, synchronize, labeled, unlabeled]
+
+jobs:
+  changelog_checker:
+    name: Check if towncrier change log entry is correct
+    runs-on: ubuntu-latest
+    steps:
+      - uses: scientific-python/[email protected]
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          BOT_USERNAME: changelog-bot