ci: add notification, when english UI strings has been updated

.github/workflows/notify_on_strings_update.yml

@@ -0,0 +1,14 @@
+name: Strings update
+on:
+  push:
+    branches: main
+    paths:
+      - "frontend/app_flowy/assets/translations/en.json"
+jobs:
+  # some way to send notification
+  - name: Notify in Discord
+    env:
+      DISCORD_WEBHOOK: ${{ secrets.DISCORD_WEBHOOK }}
+    uses: Ilshidur/action-discord@master
+    with:
+      args: '@appflowytranslators English UI strings has been updated.'