docs: fix heading size & add preview image

Signed-off-by: supr1yo <[email protected]>

BackgroundColorChanger/README.md

@@ -1,22 +1,26 @@
 # BackgroundColorChanger
+<div style="text-align:center">
+<img src='./Screenshot.png' width='500px'>
 
+</div>
+<br>
 This application is a very simple implementation of javascript. We can change the background colors using this.
 
-# Features
+## Features
 
 Change the background color of the webpage by selecting a color from a predefined list.
 
-# Installation
+## Installation
 
 No need for any installation just open the html application in your browser.
 
-# Getting started
+## Getting started
 
 1. Download index.html, style.css and script.js.
 2. Open the "index.html" file in your web browser.
 3. Start changing colors from the given palette.
 
-# Usage
+## Usage
 You will see this option for changing the background color:
 
 Color Options: Click on the color swatches to change the background color to the selected color.