Update free-programming-cheatsheets.md (#6013)

Added Scapy cheatsheet

more/free-programming-cheatsheets.md

@@ -172,6 +172,7 @@
 * [Python for Data Science Cheatsheet](https://pydatascience.org/data-science-cheatsheets/) - DataCamp (HTML and Image)
 * [Python Regex Cheatsheet](https://www.debuggex.com/cheatsheet/regex/python) - Debuggex (HTML)
 * [Python WorldWide Cheatsheet](https://cheatography.com/davechild/cheat-sheets/python/) - Cheatography (Python)
+* [Scapy Cheat Sheet](https://www.templateroller.com/template/160817/scapy-cheat-sheet-jeremy-stretch.html) - Jeremy Stretch (PDF)
 
 
 ### R