Merge pull request #190 from AY2324S2-CS2103T-W13-2/radeon2525-patch-1

Update DeveloperGuide.md

docs/DeveloperGuide.md

@@ -14,7 +14,8 @@ title: Developer Guide
   from [taskwarrior](https://github.com/GothenburgBitFactory/taskwarrior/blob/0c8edfc50e422b69abb4b78af70fc2243e227e9d/doc/man/task.1.in#L809)
 * Idea of UG navigation icons
   from [SweetRewards User Guide](https://ay2324s2-cs2103t-t13-4.github.io/tp/UserGuide.html#14-navigating-this-guide)
-
+* Implementation of Undo/Redo Commands:
+  from {https://github.com/se-edu/addressbook-level4/}
 --------------------------------------------------------------------------------------------------------------------
 
 ## **Setting up, getting started**