cmd/go/internal/help: update the documentation to match the design and implementation
The existing documentation imply that the build constraints
should be ignored after a block comments, but actually it's not.
Fixes #63502
Change-Id: I0597934b7a7eeab8908bf06e1312169b3702bf05
Reviewed-on: https://go-review.googlesource.com/c/go/+/535635 Reviewed-by: Michael Matloob <matloob@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Bryan Mills <bcmills@google.com> Reviewed-by: Mark Pictor <mark.pictor@contrastsecurity.com>
Auto-Submit: Bryan Mills <bcmills@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>