Update CHANGELOG

Author: egiurleo

Diff for: CHANGELOG.md

@@ -6,6 +6,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/) a
 
 ## [Unreleased]
 
+### Changed
+
+- The `Elsif` node has been folded into `IfNode`. A `beginning` field has been added to `IfNode` and contains a string specifying if the node represents an `if` or `elsif`.
+
 ## [5.3.0] - 2023-01-26
 
 ### Added