add docs for config

backend/development.ini.sample

@@ -186,6 +186,13 @@ wsgidav.config_path = %(here)s/wsgidav.conf
 ## return error
 # preview.jpg.restricted_dims = True
 
+### Frontend
+frontend.serve = True
+# You can set dist folder of tracim frontend. by default, system
+# will try to get it automatically according to tracim_v2 repository
+# organisation.
+# frontend.dist_folder_path = /home/user/tracim_v2/frontend/dist
+
 ###
 # wsgi server configuration
 ###