Update README with nginx and php5-fpm conf

I've been using Debian 7 and nginx + php5-fpm since December 2013 and
haven't noticed any issues.

The only thing that has noticeable impact is php scipt caching on nginx
side, but then admin makes it on purpose. By default this feature is not
enabled, but I've decided to add some info about it.

Added extra info for server_name variable for nginx, apparently this
surfaced after update from 0.20.6 to 0.20.7.