fix ROOT_URL comment

Author: wxiaoguang

custom/conf/app.example.ini

@@ -78,8 +78,9 @@ RUN_USER = ; git
 ;; Set the domain for the server
 ;DOMAIN = localhost
 ;;
-;; Overwrite the automatically generated public URL. Necessary for proxies and docker.
-;ROOT_URL = %(PROTOCOL)s://%(DOMAIN)s:%(HTTP_PORT)s/
+;; The AppURL used by Gitea to generate absolute links, defaults to "{PROTOCOL}://{DOMAIN}:{HTTP_PORT}/".
+;; Most users should set it to the real website URL of their Gitea instance.
+;ROOT_URL =
 ;;
 ;; For development purpose only. It makes Gitea handle sub-path ("/sub-path/owner/repo/...") directly when debugging without a reverse proxy.
 ;; DO NOT USE IT IN PRODUCTION!!!