docs: added additional instructions to RUN the application (#25743)

In the existing documentation only "npm start" is given as the
instruction to run the project, however the definition of the 'start'
script is not mentioned anywhere. Hence I feel it is important for the
users to know the exact contents of the 'start' scirpt and have
accordingly updated the documentation.

docs/tutorial/first-app.md

@@ -188,6 +188,15 @@ Once you've created your initial `main.js`, `index.html`, and `package.json`
 files, you can try your app by running `npm start` from your application's
 directory.
 
+**Note**: If you are building this project without downloading the example
+repository, your `start` script in `package.json` should look like this
+
+```json
+  "scripts": {
+    "start": "electron ."
+  }
+```
+
 ## Trying this Example
 
 Clone and run the code in this tutorial by using the