Fix documentation for forkProcess
Since forkProcess is disabled when number of cores to use is greater than 1, please reflect this in the documentation by replacing:
forkProcess comes with a giant warning
forkProcess is not supported by GHC runtime in the multicore setting (+RTS -N<n> greater than 1 on command line or otherwise detected)
The line "Using forkProcess in order to do executeFile is likely to work. Anything else: you're on your own. " does not seem very correct either. I think it could be removed.