Update free-courses-en.md (#9971)

* Update free-courses-en.md

Added a Theory course

* Update courses/free-courses-en.md

Co-authored-by: Eric Hellman <eric@hellman.net>

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Co-authored-by: Eric Hellman <eric@hellman.net>

courses/free-courses-en.md

@@ -1521,6 +1521,7 @@
 * [Automata Theory](https://online.stanford.edu/courses/soe-ycsautomata-automata-theory)
 * [Formal Languages & Automata Theory](https://www.youtube.com/playlist?list=PLLvKknWU7N4zvTGcw9N2_7eZSTTkryb0U) - Lalit Vashistha
 * [Intro to Theoretical Computer Science](https://www.udacity.com/course/intro-to-theoretical-computer-science--cs313) (Udacity)
+* [Theory of Computation & Automata Theory](https://www.youtube.com/playlist?list=PLBlnK6fEyqRgp46KUv4ZY69yXmpwKOIev) - Neso Academy
 
 
 ### Verilog / VHDL / SystemVerilog