doc: minor homepage tweak
doc: minor homepage tweak

Don't imply that the tour isn't browser-based.

R=adg
CC=golang-dev
http://codereview.appspot.com/5265041

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