Added PHP section to spanish version

Include the PHP section for the spansih reference books, then added the
"Manual de PHP".

free-programming-books-es.md

@@ -17,6 +17,7 @@
 * [JavaScript](#javascript)
 * [Java](#java)
 * [LaTeX](#latex)
+* [PHP](#php)
 * [Python](#python)
 * [Ruby](#ruby)
 * [Ruby on Rails](#ruby-on-rails)
@@ -108,6 +109,10 @@
 
 * [La introducción no-tan-corta a LaTeX 2ε](http://www.ctan.org/tex-archive/info/lshort/spanish)
 
+###PHP
+* [Manual de PHP (forosdelweb.com)](http://www.forosdelweb.com/wiki/Manual_de_PHP)
+
+
 ###Python
 
 * [Aprenda a pensar como un programador (con Python)](http://web.ballardini.com.ar/ai/raw-attachment/wiki/BibliografiaPython/thinkCSpy-es.pdf) (PDF)