adding course in flutter in free-courses-hi.md (#7333)

* adding course in flutter in free-courses-hi.md

* added another course in flutter

courses/free-courses-hi.md

@@ -131,6 +131,8 @@
 
 * [Complete Flutter Tutorial In Hindi By Desi Programmer](https://youtube.com/playlist?list=PLlFwzkUNmr94BF0KH7BYPL7DsZjhJRdTm) - Desi Programmer
 * [Flutter 3 tutorial in Hindi](https://youtube.com/playlist?list=PLB97yPrFwo5g-XcPlfSXSOeeby23jVAcp) - CODERS NEVER QUIT
+* [Flutter Essential Course](https://www.youtube.com/watch?v=Wdx8vwN_nWI) - freecodecamp (YouTube)
+* [Flutter Series 2020](https://www.youtube.com/playlist?list=PLDzeHZWIZsTo3Cs115GXkot28i406511Y) - CodeHelp - by Babbar (YouTube)
 * [Flutter Tutorial For Beginners in Hindi](https://youtube.com/playlist?list=PLMkkZSS5OjPIwDyHHKVex6zr008U1-sWM) - Geeks Rank