doc: we support all recent versions of OS X
doc: we support all recent versions of OS X

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/25370045

apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,apparentlymart/golang,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme