doc: Add AMD Genoa support to changelog

New entry in the changelog for AMD Genoa that is officially onboarded
and tested on Firecracker

Signed-off-by: Jack Thomson <[email protected]>

Author: JackThomson2

CHANGELOG.md

@@ -43,6 +43,8 @@ and this project adheres to
   provides the appropriate ELF Note to indicate that PVH boot mode is supported.
   Linux kernels newer than 5.0 compiled with `CONFIG_PVH=y` set this ELF Note,
   as do FreeBSD kernels.
+- [#5088](https://github.com/firecracker-microvm/firecracker/pull/5088): Added
+  AMD Genoa as a supported and tested platform for Firecracker.
 
 ### Changed