Add missing reference

documents/references.md

@@ -26,6 +26,9 @@ Includes anything from stack overflow links to notes about logic from previous w
 ### Character to Int
 <https://stackoverflow.com/a/704160>
 
+### Parse Hex Values
+<https://stackoverflow.com/a/604413>
+
 
 ## Makefile
 * Purpose of ".PHONY" - <https://stackoverflow.com/a/2145605>