Update changelog for uefi-macros

The change to `#[entry]` is mentioned in the `uefi` section already
since it's also relevant there, but worth mentioning in the
`uefi-macros` section as well so that it's clear why there's a new
version and to note that the arguments to main must now be named.

Author: nicholasbishop

CHANGELOG.md

@@ -57,6 +57,13 @@
 
 ## uefi-macros - [Unreleased]
 
+### Changed
+
+- The `#[entry]` macro now calls `BootServices::set_image_handle` to set
+  the global image handle. Due to this change, the two arguments to main
+  must both be named (e.g. `image: Handle` and `_image: Handle` are both
+  OK, but not `_: Handle`).
+
 ## uefi-services - [Unreleased]
 
 ### Added