cmd/release: package golang.org/x/tour/reader
cmd/release: package golang.org/x/tour/reader

Fixes golang/go#14184.

Change-Id: I9ce09a6b6ea4d0eb1a8c2b7cb43ecec9ee1e5109
Reviewed-on: https://go-review.googlesource.com/19797
Reviewed-by: Francesc Campoy Flores <3149fa091f5edfa916be664d7a800f2d780f07b1@golang.org>

golang/build,proppy/build,golang/build,golang/build,proppy/build,proppy/build,golang/build,proppy/build