Update sample config

docs/sample_config.yaml

@@ -954,6 +954,8 @@ password_config:
 
 # User Directory configuration
 #
+# 'enabled' defines whether users can search the user directory,
+#  defaults to True.
 # 'search_all_users' defines whether to search all users visible to your HS
 # when searching the user directory, rather than limiting to users visible
 # in public rooms.  Defaults to false.  If you set it True, you'll have to run
@@ -961,6 +963,7 @@ password_config:
 # on your database to tell it to rebuild the user_directory search indexes.
 #
 #user_directory:
+#  enabled: true
 #  search_all_users: false