📚 Add README to rust project

render-wasm/README.md

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+# render-wasm
+
+Canvas-based WebAssembly render engine for Penpot.
+
+This is a Rust crate that targets [Emscripten](https://emscripten.org/) (`wasm32-unknown-emscripten`). Underneath, it uses Skia via [custom binaries](https://github.com/penpot/skia-binaries/releases/) of the [rust-skia crate](https://github.com/rust-skia/rust-skia).
+
+## How to build
+
+With the [Penpot Development Environment](https://help.penpot.app/technical-guide/developer/devenv/) running, create a new tab in the tmux.
+
+```sh
+cd penpot/render-wasm
+./build
+```
+
+The build script will compile the project and copy the `.js` and `.wasm` files to their correct location within the frontend app.
+
+Edit your local `frontend/resources/public/js/config.js` to add the following flags:
+
+- `enable-feature-render-wasm` to enable this render engine.
+- `enable-render-wasm-dpr` (optional), to enable using the device pixel ratio.
+
+## Docs
+
+- [Serialization](./docs/serialization.md)