add BEM example link in index file

Author: satyam-seth

index.html

@@ -53,6 +53,7 @@
     <a href="./Orientation Lock/demo.html">Orientation Lock</a>
     <a href="./Scratch card effect/demo.html">Scratch card effect</a>
     <a href="./Image Sprites/demo.html">Image Sprites</a>
+    <a href="./BEM(Block, Element Modifier)/demo.html">BEM(Block, Element Modifier)</a>
 </body>
 
 </html>