Document React Native environment and Yarn setup (#133)

Fixes: #132

docs/src/guides/pre-installation.md

@@ -4,7 +4,14 @@ Better resources are available than this site for installing these dependencies.
 
 Below are a list of the dependencies, and a non-comprehensive instructions on how to get them onto your system.
 
+## Set up React Native environment
+
+Make sure you have a functional React Native environment including Node.js, Android Studio and Xcode. The [official documentation](https://reactnative.dev/docs/set-up-your-environment) contains steps to achieve this for different platforms.
+
+`uniffi-bindgen-react-native` is designed to integrate with projects created with [react-native-builder-bob](https://github.com/callstack/react-native-builder-bob). The latter assumes that you have `yarn` installed. If you don't already, you can install it by following the [official documentation](https://classic.yarnpkg.com/lang/en/docs/install).
+
 ## Install Rust
+
 If Rust isn't already installed on your system, you should install it as per the [rust-lang.org install instructions](https://www.rust-lang.org/tools/install).
 
 This will add `cargo` and `rustup` to your path, which are the main entry points into Rust.