Merge pull request #726 from cn007b/kovpak-20161124-php-books

Added book DDD in PHP.

README.md

 * [Signaling PHP](https://leanpub.com/signalingphp) - A book about catching PCNTL signals in CLI scripts by Cal Evans.
 * [The Grumpy Programmer's Guide to Building Testable PHP Applications](https://leanpub.com/grumpy-testing) - A book about building testing PHP applications by Chris Hartjes.
 * [XML Parsing with PHP](https://www.phparch.com/books/xml-parsing-with-php/) - This book covers parsing and validating XML documents, leveraging XPath expressions, and working with namespaces as well as how to create and modify XML files programmatically.
+* [Domain-Driven Design in PHP](https://leanpub.com/ddd-in-php) - Real examples written in PHP showcasing DDD Architectural Styles.
 
 ## Other Books
 *Books related to general computing and web development.*