There are no language changes in Go 1.16, so document that.
For #40700.
Fixes #42976.
Change-Id: I80b0d2ce6cf550c00c0f026ee59ac9fbce6310be
Reviewed-on: https://go-review.googlesource.com/c/go/+/275117
Trust: Dmitri Shuralyov <dmitshur@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>