Remove playdeb link

Not sure what happened but c_korn hasn't been on #getdeb on freenode in ages. The site seems to have been redesigned and no longer contains xon.

We might also wanna rephrase the part about getting into debian repos given it's not going anywhere any time soon. Something about lacking manpower/expertise might look slightly less bad than "it's WIP but nobody touched it in 5 years".

Also added a FAQ about the dedicated server nonsense based on https://forums.xonotic.org/showthread.php?tid=7941