lib/fips140: add directory and test

lib/fips140: add directory and test

This directory will hold the fips140 snapshots.
Add a README, helpful Makefile, and a test that
the checksums are correct (once we have zip files).

Change-Id: I735540ad1ce7da9a24c3a0b57b054c8340708da1
Reviewed-on: https://go-review.googlesource.com/c/go/+/629955
Reviewed-by: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@golang.org>