misc/vim: update installation instructions to work better with some Linux distributions.

Fixes issue 3308.

R=golang-dev, minux.ma
CC=golang-dev
https://codereview.appspot.com/7301086
misc/vim: make Godoc command work with "log.Print".

R=dsymonds
CC=golang-dev
https://codereview.appspot.com/7757043

Committer: David Symonds <dsymonds@golang.org>