added instructions when build fails
added instructions when build fails

It seems xbuild tries to use TargetFrameworkVersion v4.6 but that seems not to work. Forcing to use v4.5 works though!
uniaspiex/MiNET,MiPE-JP/RaNET,Vladik46/MiNET,yungtechboy1/MiNET,InPvP/MiNET