Add Operating system course (#8384)

* Add Operating system course

* Update free-courses-hi.md

courses/free-courses-hi.md

@@ -351,6 +351,7 @@
 
 ### Operating Systems
 
+* [3.2 Operating System (Complete Playlist)](https://www.youtube.com/playlist?list=PLmXKhU9FNesSFvj6gASuWmQd23Ul5omtD) - Knowledge Gate
 * [Operating System (Complete Playlist)](https://www.youtube.com/playlist?list=PLxCzCOWd7aiGz9donHRrE9I3Mwn6XdP8p) - Gate Smashers
 * [Operating Systems for Placements 2022](https://www.youtube.com/playlist?list=PLDzeHZWIZsTr3nwuTegHLa2qlI81QweYG) - CodeHelp - by Babbar