Updated config documentation in README.

Author: samdeane

README.md

@@ -202,8 +202,14 @@ configuration, by redirecting it to a file and editing it.
 
 For any source file being checked or formatted, `swift-format` looks for a
 JSON-formatted file named `.swift-format` in the same directory. If one is
-found, then that file is loaded to determine the tool's configuration. If the
-file is not found, then it looks in the parent directory, and so on.
+found, then that file is loaded to determine the tool's configuration. 
+
+If the file is not found, then it looks in the same directory for a file
+called `.no-swift-format`. The presence of this file, if found, will 
+disable all formatting (the contents of the file are ignored).
+
+If neither file is found, the search for files continues in the parent
+directory, and so on.
 
 If no configuration file is found, a default configuration is used. The
 settings in the default configuration can be viewed by running