docs: added + updated build and deployment guides (#10019)

www/apps/resources/app/medusa-cli/commands/build/page.mdx

@@ -66,7 +66,13 @@ cd .medusa/server && npm install
 - When running the application locally, make sure to copy the `.env` file from the root project's directory. In production, use system environment variables instead.
 
 ```bash npm2yarn
-cp .env .medusa/server
+cp .env .medusa/server/.env.production
+```
+
+- In the system environment variables, set `NODE_ENV` to `production`:
+
+```bash
+NODE_ENV=production
 ```
 
 - Use the `start` command to run the application: