gem5

Updated the RELEASE-NOTES.md and version number for the v20.1.0.1
hot-fix.

Change-Id: I51f7ba6f1178a2d8e80488ed2184b8735c2234a2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37116


Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Tested-by: kokoro <noreply+kokoro@google.com>