Update CHANGELOG.md (#7545)

Author: ggdouglas

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 Changelogs for `@blueprintjs/*` packages currently live in the project's Github wiki:
 
+-   [6.x Changelog](https://github.com/palantir/blueprint/wiki/6.x-Changelog)
 -   [5.x Changelog](https://github.com/palantir/blueprint/wiki/5.x-Changelog)
 -   [4.x Changelog](https://github.com/palantir/blueprint/wiki/4.x-Changelog)
 -   [3.x Changelog](https://github.com/palantir/blueprint/wiki/3.x-Changelog)