Added Linux Course (#7674)

* Added Linux Course

* Fixed Spacing

* chore: move Linux > Shell Scripting

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

courses/free-courses-bn.md

@@ -28,6 +28,7 @@
 * [Programming paradigms](#programming-paradigms)
 * [Python](#python)
 * [Scratch](#scratch)
+* [Shell scripting](#shell-scripting)
 * [TypeScript](#typescript)
 
 
@@ -217,6 +218,11 @@
 * [Scratch Programming in Bangla](https://youtube.com/playlist?list=PLym69wpbTIIEkUnqkOznZfQU6lRxebpO3) - Tamim Shahriar
 
 
+### Shell scripting
+
+* [Linux Shell Scripting Tutorial](https://www.youtube.com/playlist?list=PLMTKJq4uuKqXVg7S7XujEsONl9ZVT4X0p) - Atiq Hasan Zubu
+
+
 ### TypeScript
 
 * [TypeScript Advance Course](https://www.youtube.com/playlist?list=PLEYpvDF6qy8aesJ9a6lREDE4lcIA0iHMR) - Foyzul Karim