Fix/tictactoe docs invalid file names (#7969)

* fix: changed source file names in docs from App.js, index.js and styles.css to src/ dir

* fix: updated wrong image with the correct one with current sandbox file structure

* refactor: reverted all formatting and just just mention src folder in introductory section

* Reverted changes tutorial-tic-tac-toe.md

* added enhanced image of sandbox

Author: mtayyabrawan

public/images/tutorial/react-starter-code-codesandbox.png

@@ -283,7 +283,7 @@ In CodeSandbox you'll see three main sections:
 
 ![CodeSandbox with starter code](../images/tutorial/react-starter-code-codesandbox.png)
 
-1. The _Files_ section with a list of files like `App.js`, `index.js`, `styles.css` and a folder called `public`
+1. The _Files_ section with a list of files like `App.js`, `index.js`, `styles.css` in `src` folder and a folder called `public`
 1. The _code editor_ where you'll see the source code of your selected file
 1. The _browser_ section where you'll see how the code you've written will be displayed