database/sql: link to driver wiki page
database/sql: link to driver wiki page

Fixes issue 5127

R=golang-dev, adg
CC=golang-dev
https://codereview.appspot.com/8011044

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