Flutter bangla course add (#6172)

* Flutter bangla course add

add Bangla flutter tutorial course

* updated

books/free-programming-books-bn.md

@@ -9,6 +9,7 @@
 * [Competitive Programming](#competitive-programming)
 * [CSS](#css)
 * [Dart](#dart)
+* [Flutter](#flutter)
 * [Git](#git)
 * [HTML](#html)
 * [Java](#java)
@@ -78,6 +79,12 @@
 * [Dart All You Need To Know](https://www.youtube.com/playlist?list=PL_XxuZqN0xVC2-nXUrvpcQEz3FgCSIQHT) - Stack Learner
 
 
+### Flutter
+
+* [Flutter Bangla Tutorial](https://www.youtube.com/playlist?list=PLg87mxEuu8-692INeEsxudyVifz7M3efy) - Techno BD XYZ
+* [Flutter Tutorial Bangla](https://www.youtube.com/playlist?list=PLZJlOXxGEkuyZQ-vA7B5vpvvtWU3Upo6p) - Soykot Hosen
+
+
 ### Git
 
 * [Crash Course - সহজ বাংলায় Git & GitHub - Bangla ( বাংলা ) Tutorial](https://www.youtube.com/watch?v=oe21Nlq8GS4&t=182s) - Learn with Sumit