templates: Add macro for appending branch names to Git webhook URLs.

templates/zerver/help/include/git-webhook-url-with-branches.md

@@ -0,0 +1,5 @@
+You can also limit the branches you receive notifications for by
+specifying them in a comma-separated list at the end of the URL,
+like so:
+
+`{{ external_api_uri_subdomain }}{{ integration_url }}?api_key=abcdefgh&stream={{ integration_name }}&branches=master,development`

tools/linter_lib/custom_check.py

@@ -428,6 +428,7 @@ def build_custom_checkers(by_lang):
             "zerver/webhooks/solano/doc.md",
             "zerver/webhooks/trello/doc.md",
             "zerver/webhooks/papertrail/doc.md",
+            "templates/zerver/help/include/git-webhook-url-with-branches.md",
         }
         for fn in by_lang['md']:
             max_length = None