note about xAPI 401 unauthorized

I was having problems to get working xAPI endpoint after migrate from Vaprobash (Vagrant) Ubuntu 12.04 to 14.04 due to 401 unauthorized requests. Debugging I noticed neither PHP_AUTH_USER nor PHP_AUTH_PW are available. Finally googling I found the work around for this setup and I've included a note in statement documentation.

Special thanks to [Rich](http://stackoverflow.com/users/8261/rich) http://stackoverflow.com/questions/17488656/zend-server-windows-authorization-header-is-not-passed-to-php-script have the applied solution