$ gotip tool -h says:

  For more about each tool command, see 'go tool command -h'.

But it's better to suggest

  go doc cmd/<command>

Fixes #18313

Change-Id: I0a36d585906a5e1879e5b7927d1b6173e97cb500
Reviewed-on: https://go-review.googlesource.com/55990Reviewed-by: Ian Lance Taylor <iant@golang.org>