Added Distributed Systems and Bash Shell Scripting in english (#6140)

* Added Distributed Systems and Bash Shell Scripting in english

* Added Distributed Systems tutorial

courses/free-courses-en.md

@@ -656,6 +656,7 @@
 * [LouvainX Paradigms of Computer Programming – Abstraction and Concurrency](https://www.edx.org/course/paradigms-computer-programming-louvainx-louv1-2x-1#!)
 * [LouvainX Paradigms of Computer Programming – Fundamentals](https://www.edx.org/course/paradigms-computer-programming-louvainx-louv1-1x-1)
 * [Made with ML](https://madewithml.com) - Goku Mohandas (Applied ML · MLOps · Production)
+* [MIT 6.824 Distributed Systems (Spring 2020)](https://www.youtube.com/playlist?list=PLrw6a1wE39_tb2fErI4-WkMbsvGQk9_UB) - MIT 6.824 Distributed Systems
 * [MIT Numerical Methods (2014)](http://www.iitg.ernet.in/kartha/CE601-14/CourseSchedule.htm)
 * [MIT's Computer Language Engineering](http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-035-computer-language-engineering-sma-5502-fall-2005/lecture-notes/)
 * [MIT's Introduction to Algorithms](http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-006-introduction-to-algorithms-fall-2011/)