Invoke docs (#8373)

* Add separate docs page for invoke

* More info on available tasks

* More info

* Strict mode is strict

docs/mkdocs.yml

@@ -100,6 +100,7 @@ nav:
     - Serving Files: start/serving_files.md
     - User Accounts: start/accounts.md
     - Data Backup: start/backup.md
+    - Invoke: start/invoke.md
     - Migrating Data: start/migrate.md
     - Advanced Topics: start/advanced.md
   - Parts: