cmd/go/internal/get: improve -insecure deprecation docs
Updates #37519
Change-Id: I212607f1839b729d7da24b1258e56997b13ad830
GitHub-Last-Rev:
db6d3c835bdf867a0b18f115276210e3a05902ed
GitHub-Pull-Request: golang/go#41613
Reviewed-on: https://go-review.googlesource.com/c/go/+/257157
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Jay Conrod <jayconrod@google.com>
Trust: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>