Update changelog

Author: aeisenberg

extensions/ql-vscode/CHANGELOG.md

@@ -5,6 +5,7 @@
 - Report error when selecting invalid database.
 - Add descriptive message for database archive import failure.
 - Respect VSCode's i18n locale setting when formatting dates and sorting strings.
+- Allow the opening of large Sarif files externally from VSCode.
 
 ## 1.2.2 - 8 June 2020