Adding Playlist Explaining Sliding Window Algorithm (#7503)

* Adding YT Playlist Explaining Sliding Window Algo

This is one of the best playlist to study and learn about the Sliding Window Algorithm

* Removed the pipe character

courses/free-courses-hi.md

@@ -56,6 +56,7 @@
 * [Recursion & Backtracking - Level 1](https://www.youtube.com/playlist?list=PL-Jc9J83PIiFxaBahjslhBD1LiJAV7nKs) - Pepcoding
 * [Recursion & Backtracking - Level 2](https://www.youtube.com/playlist?list=PL-Jc9J83PIiHO9SQ6lxGuDsZNt2mkHEn0) - Pepcoding
 * [Recursion Playlist \| Coding \| Interview Questions \| Algorithm \| Tutorials](https://www.youtube.com/playlist?list=PL_z_8CaSLPWeT1ffjiImo0sYTcnLzo-wY) - Aditya Verma
+* [Sliding Window Algorithm - Face to Face Interviews](https://youtube.com/playlist?list=PL_z_8CaSLPWeM8BDJmIYDaoQ5zuwyxnfj) - Aditya Verma
 * [Time and Space - Level 1](https://www.youtube.com/playlist?list=PL-Jc9J83PIiFc7hJ5eeCb579PS8p-en4f) - Pepcoding