README.md: add links to license files

Closes #1367

Author: emilk

README.md

@@ -5,8 +5,8 @@
 [![Documentation](https://docs.rs/egui/badge.svg)](https://docs.rs/egui)
 [![unsafe forbidden](https://img.shields.io/badge/unsafe-forbidden-success.svg)](https://github.com/rust-secure-code/safety-dance/)
 [![Build Status](https://github.com/emilk/egui/workflows/CI/badge.svg)](https://github.com/emilk/egui/actions?workflow=CI)
-![MIT](https://img.shields.io/badge/license-MIT-blue.svg)
-![Apache](https://img.shields.io/badge/license-Apache-blue.svg)
+[![MIT](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/emilk/egui/blob/master/LICENSE-MIT)
+[![Apache](https://img.shields.io/badge/license-Apache-blue.svg)](https://github.com/emilk/egui/blob/master/LICENSE-APACHE)
 [![Discord](https://img.shields.io/discord/900275882684477440?label=egui%20discord)](https://discord.gg/JFcEma9bJq)
 
 👉 [Click to run the web demo](https://www.egui.rs/#demo) 👈