cmd/go: add pointer to build flags in "go get" docs
Fixes #67728
Change-Id: Ifbdee77dcebd865eac9501ec4615128eb3a9c9c0
Reviewed-on: https://go-review.googlesource.com/c/go/+/590797
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com> Reviewed-by: Michael Matloob <matloob@golang.org>
Commit-Queue: Ian Lance Taylor <iant@google.com>