content/static/doc: add code.html

See deletion CL here: https://golang.org/cl/199057

Updates golang/go#33637
Updates golang/go#29206

Change-Id: I992a6f3222b6327927578111ad71bdf3653adf78
Reviewed-on: https://go-review.googlesource.com/c/website/+/199058
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: jeanbza