Mark visual elements task as completed in TODO.md

Author: jedisct1

www/TODO.md

@@ -15,7 +15,7 @@ This document outlines planned improvements and future tasks for the IPCrypt web
 ### Design Improvements
 
 - [x] Create a proper favicon and apple-touch-icon
-- [ ] Add more visual elements to explain encryption modes
+- [x] Add more visual elements to explain encryption modes
 - [ ] Improve mobile navigation for smaller screens
 - [ ] Enhance print styles for better documentation printing