CHANGELOG.md: Some additional affordances in various xl subcommands

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@citrix.com>
---
CC: Ian Jackson <ian.jackson@citrix.com>

CHANGELOG.md

@@ -25,6 +25,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
  - Factored out HVM-specific shadow code, improving code clarity and reducing the size of PV-only hypervisor builds
  - Added XEN_SCRIPT_DIR configuration option to specify location for Xen scripts, rather than hard-coding /etc/xen/scripts
  - xennet: Documented a way for the backend (or toolstack) to specify MTU to the frontend
+ - Some additional affordances in various xl subcommands.
 
 ### Removed / support downgraded