doc: fix old broken link
doc: fix old broken link

The Camlistore code tree rearranged after the go tool came
out. (I didn't know this link was here until I saw it in
some logs.)

R=adg
CC=golang-dev
https://codereview.appspot.com/7374043

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang