docs: Mentioning npm run server:dev command

Author: Lalit3716

content/first-steps.md

@@ -100,3 +100,10 @@ $ npm run start
 ```
 
 This command starts the app with the HTTP server listening on the port defined in the `src/main.ts` file. Once the application is running, open your browser and navigate to `http://localhost:3000/`. You should see the `Hello World!` message.
+
+To watch changes in your files, you can run the following command to start the application:
+```bash
+$ npm run start:dev
+```
+
+This command will watch your files for changes and will automatically reload the server.