misc: added news on RISC-V to RELEASE-NOTES.md.

Change-Id: I9b60cd2f533e6d4ce677e8a9b7bb5a5698e51c61
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/28448
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed