Add PHP RFCs page.

README.md

 ## PHP Internals Reading
 *Reading materials related to the PHP internals or performance.*
 
+* [PHP RFCs](https://wiki.php.net/rfc) - The home of PHP RFCs (Request for Comments).
 * [Print vs Echo, Which One is Faster?](http://fabien.potencier.org/article/8/print-vs-echo-which-one-is-faster) - An article about print and echo performance.
 * [The PHP Ternary Operator. Fast or Not?](http://fabien.potencier.org/article/48/the-php-ternary-operator-fast-or-not) - An article ternary performance.
 * [Disproving the Single Quotes Myth](http://nikic.github.com/2012/01/09/Disproving-the-Single-Quotes-Performance-Myth.html) - An article about performance of single and double quoted strings.