Update README to maintained Tetra integration (#4606)

Original integration https://github.com/tesselode/egui-tetra is
archived, so I forked and updated for latest `egui` and `tetra`.

README.md

@@ -201,7 +201,7 @@ These are the official egui integrations:
 * [`egui-macroquad`](https://github.com/optozorax/egui-macroquad) for [macroquad](https://github.com/not-fl3/macroquad)
 * [`egui-miniquad`](https://github.com/not-fl3/egui-miniquad) for [Miniquad](https://github.com/not-fl3/miniquad)
 * [`egui_speedy2d`](https://github.com/heretik31/egui_speedy2d) for [Speedy2d](https://github.com/QuantumBadger/Speedy2D)
-* [`egui-tetra`](https://crates.io/crates/egui-tetra) for [Tetra](https://crates.io/crates/tetra), a 2D game framework
+* [`egui-tetra2`](https://crates.io/crates/egui-tetra2) for [Tetra](https://crates.io/crates/tetra), a 2D game framework
 * [`egui-winit-ash-integration`](https://github.com/MatchaChoco010/egui-winit-ash-integration) for [winit](https://github.com/rust-windowing/winit) and [ash](https://github.com/MaikKlein/ash)
 * [`fltk-egui`](https://crates.io/crates/fltk-egui) for [fltk-rs](https://github.com/fltk-rs/fltk-rs)
 * [`ggegui`](https://github.com/NemuiSen/ggegui) for the [ggez](https://ggez.rs/) game framework