Update README requirements for supported subfolders

Author: christopher-hopper

README.md

@@ -50,7 +50,8 @@ Create a composer package of your coding standard by adding a `composer.json` fi
 ```
 
 Requirements:
-* The repository may contain one or more standards. Each in their separate directory in the root of your repository.
+* The repository may contain one or more standards.
+* Each standard can have a separate directory no deeper than 3 levels from the repository root.
 * The package `type` must be `phpcodesniffer-standard`. Without this, the plugin will not trigger.
 
 [this]: https://github.com/squizlabs/PHP_CodeSniffer/wiki/Coding-Standard-Tutorial