bind/js: Adds contribution guide

bindings/javascript/docs/CONTRIBUTING.md

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+# Contributing
+
+So you want to contribute to Limbo's binding for the ~second~ best language in the world? Awesome.
+
+First things first you'll need to install [napi-rs](https://napi.rs/), follow the instructions [here](https://napi.rs/docs/introduction/getting-started) althought is highly recommended to use `yarn` with:
+
+```sh
+yarn global add @napi-rs/cli
+```
+
+Run `yarn build` to build our napi project and run `yarn test` to run our test suite, if nothing breaks you're ready to start!
+
+## API
+
+You can check the API docs [here](./API.md), it aims to be fully compatible with [better-sqlite](https://github.com/WiseLibs/better-sqlite3/) and borrows some things from [libsql](https://github.com/tursodatabase/libsql-js). So if you find some incompability in behaviour and/or lack of functions/attributes, that's an issue and you should work on it for a great good :)
+
+## Code Structure
+
+The Rust code for the bind is on [lib.rs](../src/lib.rs). It's exposed to JS users through [wrapper](../wrapper.js), where you can
+use some JS' ~weirdness~ facilities, for instance, since Rust doesn't have variadic functions the wrapper enables us to "normalize" `bindParameters` into an array.
+
+All tests should be within the [__test__](../__test__/) folder.
+
+# Before open a PR
+
+Please be assured that:
+
+- Your fix/feature has a test checking the new behaviour;
+- Your code follows Rust's conventions with `cargo fmt`;
+- If applicable, update the [API docs](./API.md) to match the current implementation;
+