doc: document GOEXPERIMENT=aliastypeparams in release notes

For #65614.

Change-Id: I05b20a80b1163e1d3927c2f763ef6b7d20e6a937
Reviewed-on: https://go-review.googlesource.com/c/go/+/590617


Reviewed-by: Robert Griesemer <gri@google.com>
Auto-Submit: Robert Griesemer <gri@google.com>
TryBot-Bypass: Robert Griesemer <gri@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>