Add note about running web servers

[ysbaddaden]

Prax redirects traffic from port 80 to port 20559 and port 443 to port 20558 (using iptables rules), which may conflict with running web servers (like nginx or apache). We should had a note about it the README or in a FAQ on the wiki —and link to solutions to configure a webserver to proxy to Prax if we need them running.

As reported in the comments of #77.

[HLFH]

Well. Prax is messing the server and apache2. Big issue. Solved by removing Prax & flushing iptables rules with a script.