Add CHANGELOG entry

extensions/ql-vscode/CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## [UNRELEASED]
 
+- Warn users when their VS Code version is too old to support all features in the vscode-codeql extension. [#1674](https://github.com/github/vscode-codeql/pull/1674)
+
 ## 1.7.4 - 29 October 2022
 
 No user facing changes.