cmd/go/internal/modget: improve GOINSECURE docs
Recommend use of GOINSECURE over -insecure flang and clarify that GOINSECURE
environment variable does not also imply GONOSUMDB.
Updates #37519 by adding documentation as discussed.
Change-Id: Ia8ab6b3ed1aa559343b72e4ca76c372ee6bf1941
GitHub-Last-Rev:
8d86991f0c1a759f45568c1cc6ef6dc41225f2ba
GitHub-Pull-Request: golang/go#38572
Reviewed-on: https://go-review.googlesource.com/c/go/+/229223
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>