Add links to the changelogs for other crates.
(Tested via the GH web interface.)
All notable changes to the egui crate will be documented in this file.
-NOTE: `eframe`, `egui_web` and `egui_glium` has their own changelogs!
+NOTE: [`eframe`](eframe/CHANGELOG.md), [`egui_web`](egui_web/CHANGELOG.md) and [`egui_glium`](egui_glium/CHANGELOG.md) has their own changelogs!
## Unreleased
