Update free-courses-hi.md (#8531)

Added a youtube playlist for Flask

courses/free-courses-hi.md

@@ -418,6 +418,7 @@
 
 #### Flask
 
+* [[Hindi] Flask Tutorial For Beginners 2020](https://www.youtube.com/playlist?list=PLkPmSWtWNIyQ-_mlHIQho9nCnxdbvnQIl) - Knowledge Shelf
 * [Web Development Using Flask and Python](https://www.youtube.com/playlist?list=PLu0W_9lII9agAiWp6Y41ueUKx1VcTRxmf) - CodeWithHarry