Add Ruby cheat sheet (#8084)

* Add Ruby cheat sheet

* Update free-programming-cheatsheets.md

more/free-programming-cheatsheets.md

@@ -343,6 +343,7 @@
 ### Ruby
 
 * [Ruby Cheat Sheet](https://www.codeconquest.com/wp-content/uploads/Ruby-Cheat-Sheet-by-CodeConquestDOTcom.pdf) - CodeConquest.com (PDF)
+* [Ruby monstas Ruby cheat sheet](https://rubymonstas.ch/materials/canonical/session05/session5-ruby-cheat-sheet.pdf) - rubymonstas.ch (PDF)
 
 
 ### Rust