Remove wit-bindgen from dependencies and add note about re-bindgen

Author: kateinoigakukun

CONTRIBUTING.md

@@ -0,0 +1,9 @@
+## Re-bindgen from `.wit` files
+
+If you update [`*.wit`](https://github.com/WebAssembly/component-model/blob/ed90add27ae845b2e2b9d7db38a966d9f78aa4c0/design/mvp/WIT.md), which describe the interface of a WebAssembly module, either imported or exported, you need to re-generate glue code from `*.wit`.
+
+To re-generate them, you need to install the Rust compiler `rustc` and Cargo, then run `rake check:bindgen`.
+
+The rake task installs [`wit-bindgen`](https://github.com/bytecodealliance/wit-bindgen) on demand, then just execute it for each generated code
+
+If you see `missing executable: cargo`, please make sure `cargo` is installed correctly in your `PATH`.

README.md

@@ -69,7 +69,6 @@ If you want to build Ruby for WebAssembly from source yourself, follow the below
 
 ### Dependencies
 
-- [wit-bindgen](https://github.com/bytecodealliance/wit-bindgen): A language bindings generator for `wit` used in the npm packages. Install in `PATH`.
 - [wasi-sdk](https://github.com/WebAssembly/wasi-sdk): Only for building for WASI target. Set `WASI_SDK_PATH` environment variable to the directory of wasi-sdk.
 - [Binaryen](https://github.com/WebAssembly/binaryen): Only for building for WASI target. Install `wasm-opt` in `PATH`
 - [wasi-vfs](https://github.com/kateinoigakukun/wasi-vfs): A virtual filesystem layer for WASI. Install CLI tool in `PATH`. Set `LIB_WASI_VFS_A` environment variable to the path to `libwasi_vfs.a`.