Add downloads badge to some game engines

When evaluating a game engine, popularity is a very valuable metric.

README.md

@@ -1190,15 +1190,15 @@ See also [Are we game yet?](https://arewegameyet.rs)
   * [amethyst/specs](https://github.com/amethyst/specs) — Specs Parallel ECS [![build badge](https://api.travis-ci.org/amethyst/specs.svg?branch=master)](https://travis-ci.org/amethyst/specs)
   * [legion](https://github.com/amethyst/legion) — A feature rich high performance ECS library with minimal boilerplate [![build badge](https://github.com/amethyst/legion/workflows/CI/badge.svg?branch=master)](https://github.com/amethyst/legion/actions)
 * Game Engines
-  * [Amethyst](https://amethyst.rs) — Data-oriented game engine - [![Crates.io](https://img.shields.io/crates/v/amethyst)](https://crates.io/crates/amethyst) [![license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/amethyst/amethyst/blob/main/COPYING)
+  * [Amethyst](https://amethyst.rs) — Data-oriented game engine - [![Crates.io](https://img.shields.io/crates/v/amethyst)](https://crates.io/crates/amethyst) [![license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/amethyst/amethyst/blob/main/COPYING) [![Crates.io](https://img.shields.io/crates/d/amethyst.svg)](https://crates.io/crates/amethyst)
   * [Bevy](https://github.com/bevyengine/bevy) is a refreshingly simple data-driven game engine built in Rust. - [![Crates.io](https://img.shields.io/crates/v/bevy.svg)](https://crates.io/crates/bevy)
 [![license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/bevyengine/bevy/blob/master/LICENSE)
 [![Crates.io](https://img.shields.io/crates/d/bevy.svg)](https://crates.io/crates/bevy)
-  * [ggez](https://github.com/ggez/ggez) — A lightweight game framework for making 2D games with minimum friction - [![Crates.io](https://img.shields.io/crates/v/ggez.svg)](https://crates.io/crates/ggez) [![license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/ggez/ggez/blob/master/LICENSE)
+  * [ggez](https://github.com/ggez/ggez) — A lightweight game framework for making 2D games with minimum friction - [![Crates.io](https://img.shields.io/crates/v/ggez.svg)](https://crates.io/crates/ggez) [![license](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/ggez/ggez/blob/master/LICENSE) [![Crates.io](https://img.shields.io/crates/d/ggez.svg)](https://crates.io/crates/ggez)
   * [harmony](https://github.com/StarArawn/harmony) — A modern 3D/2D game engine that uses wgpu
-  * [Kiss3d](http://kiss3d.org) — A Keep It Simple, Stupid 3d graphics engine written with Rust
+  * [Kiss3d](http://kiss3d.org) — A Keep It Simple, Stupid 3d graphics engine written with Rust [![Crates.io](https://img.shields.io/crates/d/kiss3d.svg)](https://crates.io/crates/kiss3d)
   * [oxidator](https://github.com/Ruddle/oxidator) — A real time strategy game/engine written with Rust and WebGPU
-  * [Piston](https://www.piston.rs/) — [![Crates.io](https://img.shields.io/crates/v/piston.svg?style=flat-square)](https://crates.io/crates/piston) [![Crates.io](https://img.shields.io/crates/l/piston.svg)](https://github.com/PistonDevelopers/piston/blob/master/LICENSE)
+  * [Piston](https://www.piston.rs/) — [![Crates.io](https://img.shields.io/crates/v/piston.svg?style=flat-square)](https://crates.io/crates/piston) [![Crates.io](https://img.shields.io/crates/l/piston.svg)](https://github.com/PistonDevelopers/piston/blob/master/LICENSE) [![Crates.io](https://img.shields.io/crates/d/piston.svg)](https://crates.io/crates/piston)
   * [Unrust](https://github.com/unrust/unrust) — unrust — A pure rust based (webgl 2.0 / native) game engine
 * [Godot](https://godotengine.org/)
   * [godot-rust/godot-rust](https://github.com/godot-rust/godot-rust) [[gdnative](https://crates.io/crates/gdnative)] - Rust bindings to the Godot game engine [![build badge](https://api.travis-ci.com/godot-rust/godot-rust.svg?branch=master)](https://travis-ci.com/github/godot-rust/godot-rust)