Update README.md to include Codemia as a tool to practice system design problems

codemia.io is a platform for practicing and studying system design problem. Users can practice alone via AI tool or share their solution on the platform to get human feedback as well.

Author: markqian

README.md

@@ -1245,6 +1245,7 @@ Mock Interviews:
 - [interviewing.io: Practice mock interview with senior engineers](https://interviewing.io) - anonymous algorithmic/systems design interviews with senior engineers from FAANG anonymously
 - [Meetapro: Mock interviews with top FAANG interviewers](https://meetapro.com/?utm_source=ciu) - an Airbnb-style mock interview/coaching platform.
 - [Hello Interview: Mock Interviews with Expert Coaches and AI](https://www.hellointerview.com/?utm_source=ciu) - interview directly with AI or with FAANG staff engineers and managers.
+- [Codemia: Practice system design problems with AI or community solutions and feedback](https://codemia.io/?utm_source=ciu) - Practice system design problems via AI practice tool. Share your solution with the community to get human feedback as well.
 
 ## Be thinking of for when the interview comes