Update free-courses-pt_BR.md (#7916)

Added course about Shell GNU

courses/free-courses-pt_BR.md

@@ -323,6 +323,7 @@
 ### Shell
 
 * [Conceitos de Programação em Shell Script](https://www.udemy.com/conceitos-de-programacao-em-shell-script/) - TemWeb (Udemy)
+* [Curso Shell GNU](https://www.youtube.com/playlist?list=PLXoSGejyuQGqJEEyo2fY3SA-QCKlF2rxO) - debxp (YouTube)
 
 
 ### Swift