docs: add notes about local tooling (#5617)

CONTRIBUTING.md

@@ -39,7 +39,24 @@ When contributing to Better Auth:
    cd better-auth
    ```
 3. Install Node.js (LTS version recommended)
-4. Install pnpm if you haven't already:
+
+   > **Note**: This project is configured to use [nvm](https://github.com/nvm-sh/nvm) to manage the local Node.js version, as such this is simplest way to get you up and running.
+
+   Once installed, use:
+
+   ```bash
+   $ nvm install
+   $ nvm use
+   ```
+
+   Alternatively, see Node.js [installation](https://nodejs.org/en/download) for other supported methods.
+
+4. Install `pnpm` if you haven't already:
+
+   > **Note:** This project is configured to manage [pnpm](https://pnpm.io/) via [corepack](https://github.com/nodejs/corepack). Once installed, upon usage you'll be prompted to install the correct pnpm version
+
+   Alternatively, use `npm` to install it:
+
    ```bash
    npm install -g pnpm
    ```