Add more books.

README.md

@@ -647,16 +647,20 @@ Various resources, such as books, websites and articles, for improving your PHP
 *Fantastic PHP-related books.*
 
 * [Scaling PHP Applications](http://www.scalingphpbook.com) - An ebook about scaling PHP applications by Steve Corona.
+* [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.
 * [Grumpy PHPUnit](https://leanpub.com/grumpy-phpunit) - A book about unit testing with PHPUnit by Chris Hartjes.
 * [Mastering Object-Orientated PHP](http://www.brandonsavage.net) - A book about object-orientated PHP by Brandon Savage.
 * [Signaling PHP](https://leanpub.com/signalingphp) - A book about catching PCNTL signals in CLI scripts by Cal Evans.
 * [Securing PHP: Core Concepts](https://leanpub.com/securingphp-coreconcepts) - A book about common security terms and practices for PHP by Chris Cornutt.
+* [Modernising Legacy Applications in PHP](https://leanpub.com/mlaphp) - A book about modernising legacy PHP applications by Paul M. Jones.
 
 ## Other Books
 *Books related to general computing and web development.*
 
 * [The Linux Command Line](http://linuxcommand.org/tlcl.php) - A book about the Linux command line by William Shotts.
 * [Understanding Computation](http://computationbook.com) - A book about computation theory by Tom Stuart.
+* [The Tangled Web — Securing Web Applications](http://www.amazon.ca/The-Tangled-Web-Securing-Applications/dp/1593273886) - A book about securing web applications by Michal Zalewski.
+* [Elasticsearch: The Definitive Guide](http://www.elasticsearch.org/guide/) - A guide to working with Elasticsearch by Clinton Gormley and Zachary Tong.
 
 ## PHP Videos
 *Fantastic PHP-related videos.*