Add MailCatcher.

README.md

 * [DBV](http://dbv.vizuina.com/) - A database version control application.
 * [PHP Queue](https://github.com/CoderKungfu/php-queue) - An application for managing queueing backends.
 * [Composer as a Service](http://composer.borreli.com/) - A tool for downloading Composer packages as a zip file.
+* [MailCatcher](https://github.com/sj26/mailcatcher) - A web tool for capturing and viewing emails.
 
 # Resources
 Various resources, such as books, websites and articles, for improving your PHP development skills and knowledge.