chore: add notice about `build` step in contribution guide

.github/contributing.md

@@ -34,12 +34,14 @@ $ pnpm install
 
 ### Setup VitePress Dev Environment
 
-You may start VitePress local dev environment by running `pnpm run dev`.
+At first, execute the `pnpm run build` command.
 
 ```bash
-$ pnpm run dev
+$ pnpm run build
 ```
 
+You only need to do this once for your fresh project. It copies required files and makes sure everything is in place. After this, you only need to run `dev` related commands.
+
 The easiest way to start testing out VitePress is to tweak the VitePress docs. You may run `pnpm run docs` to boot up VitePress documentation site locally, with live reloading of the source code.
 
 ```bash
@@ -47,3 +49,9 @@ $ pnpm run docs
 ```
 
 After executing the above command, visit http://localhost:3000 and try modifying the source code. You'll get live update.
+
+If you don't need docs site up and running, you may start VitePress local dev environment with `pnpm run dev`.
+
+```bash
+$ pnpm run dev
+```