Updated README.md to include code docs

Author: Dimitri van Heesch

README.md

@@ -33,6 +33,8 @@ Developers
 
 * Coverity Scan Build Status: <a href="https://scan.coverity.com/projects/2860"> <img alt="Coverity Scan Build Status" src="https://scan.coverity.com/projects/2860/badge.svg"/> </a>
 
+* Doxygen's Doxygen Documentation: <a href="https://codedocs.xyz/doxygen/doxygen/"><img src="https://codedocs.xyz/doxygen/doxygen.svg"/></a>
+
 * Install
   * Quick install see (./INSTALL) 
   * else http://www.doxygen.org/manual/install.html