docs: add contribution instructions

CONTRIBUTING.md

@@ -0,0 +1,32 @@
+
+## Contributing
+
+To contribute to Nuxt Test Utils, you need to set up a local environment.
+
+1. [Fork](https://help.github.com/articles/fork-a-repo) the [`nuxt/test-utils`](https://github.com/nuxt/test-utils) repository to your own GitHub account and then [clone](https://help.github.com/articles/cloning-a-repository) it to your local device.
+1. Enable [Corepack](https://github.com/nodejs/corepack) to have access to `pnpm`
+   ```bash [Terminal]
+   corepack enable
+   ```
+1. Run `pnpm install` to install the dependencies with pnpm:
+   ```bash [Terminal]
+   pnpm install && pnpm playwright install chromium
+   ```
+1. Activate the passive development system
+   ```bash [Terminal]
+   pnpm dev:prepare
+   ```
+1. Check out a branch where you can work and commit your changes:
+   ```bash [Terminal]
+   git checkout -b my-new-branch
+   ```
+
+Then, test your changes against the examples before submitting a pull request.
+
+```bash
+pnpm prepack
+pnpm test:examples
+pnpm dev:prepare
+```
+
+Read more in the [Nuxt Contribution Guide](https://nuxt.com/docs/community/contribution#how-to-contribute).