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
gofmt: explain why lower bounds aren't automatically simplified

Full credit goes to gri and rsc for their explanations.

R=golang-dev, r
CC=golang-dev
https://codereview.appspot.com/14229043

Committer: Rob Pike <r@golang.org>