[x/tour] go-tour: Fix introduction slide and a formatting error.
[x/tour] go-tour: Fix introduction slide and a formatting error.

R=adg
CC=golang-dev
https://golang.org/cl/7377055
X-Tour-Commit: a9fef78bf8606629b6d06c3a54436f6e6a34d114

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website