Added to free-programming-cheatsheets.md (#5986)

* Update free-programming-playgrounds.md

* Update free-programming-playgrounds.md

* Update free-programming-playgrounds.md

* Update free-programming-cheatsheets.md

* Update free-programming-cheatsheets.md

* Update more/free-programming-cheatsheets.md

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

* Update more/free-programming-cheatsheets.md

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

* Update more/free-programming-cheatsheets.md

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

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

more/free-programming-cheatsheets.md

@@ -3,6 +3,7 @@
 * [Artificial Intelligence](#artificial-intelligence)
 * [Bash](#bash)
 * [C](#c)
+* [C#](#c-sharp)
 * [C++](#cpp)
 * [Clojure](#clojure)
 * [Data Science](#data-science)
@@ -45,6 +46,11 @@
 * [The C Cheat Sheet: An Introduction to Programming in C](https://sites.ualberta.ca/~ygu/courses/geoph624/codes/C.CheatSheet.pdf) - Andrew Sterian (PDF)
 
 
+### <a name="c-sharp"></a>C#
+
+* [C# Cheat Sheet](https://simplecheatsheet.com/tag/c-cheat-sheet-1/) - Simple Cheat Sheet (HTML)
+
+
 ### <a name="cpp"></a>C++
 
 * [C++ Quick Reference](http://www.hoomanb.com/cs/quickref/CppQuickRef.pdf) - Hooman Baradaran (PDF)