Update 09-loops.md

Added a link to a blog

Author: razorblade23

curriculum/01-foundations/09-loops.md

@@ -103,4 +103,7 @@ Ready to test your knowledge? Try writing a `for` loop that prints out the lette
 
 ```python interactive
 my_name = "" # write you name here
-```
+```
+
+## Deep dive
+https://www.stratascratch.com/blog/python-loops-explained-here-is-how-to-master-them