doc: remove link to PackageVersioning wiki
doc: remove link to PackageVersioning wiki

That page may be fine for experienced Go programmers
but it's not really targeting new programmers.
There's too much we don't know yet.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/14345043

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