Changed header level in readme

Author: vssr

README.md

@@ -3,7 +3,7 @@
 # composer-file-installer
 Install files in a project as part of a `composer install` or `composer update`. Uses the[mediact/file-mapping](https://github.com/mediact/file-mapping) package for moving files according to a source -> destination mapping. The Composer `IOInterface` supplies the file installer with the capabiliy to write the files and supply end-users with output messages.
 
-# Usage example
+## Usage example
 ```php
 <?php
 // Create a file mapping.