README: Mention possibility of over-tuning to c2d
README: Mention possibility of over-tuning to c2d

This was developed and tested on a MacBook Pro with a 2.67GHz Core 2 Duo.
It's possible it does unexpectedly worse on other machines.

LnxPrgr3/crossfeed,LnxPrgr3/message_queue,LnxPrgr3/crossfeed