add discord link

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-book/src/00-overview.md

@@ -112,6 +112,12 @@ simple. We recommend you to think carefully about your implementation and write
 * You can use `cargo x scheck` to run all test cases and do style check in your codebase.
 * You can use `cargo x copy-test dayX` to copy test cases to the starter code.
 
+## Community
+
+You may join skyzh's Discord server and study with the mini-lsm community.
+
+[![Join skyzh's Discord Server](https://dcbadge.vercel.app/api/server/ZgXzxpua3H)](https://skyzh.dev/join/discord)
+
 ## About the Author
 
 As of writing (at the end of 2022), Chi is a first-year master's student in Carnegie Mellon University. He has 5 years'
@@ -131,4 +137,4 @@ vectorized expression framework if you are also interested in that topic.
 [15445-course]: https://15445.courses.cs.cmu.edu/fall2022/
 [tweet]: https://twitter.com/andy_pavlo/status/1598137241016360961
 [type-exercise]: https://github.com/skyzh/type-exercise-in-rust
-[bustub]: https://github.com/cmu-db/bustub
+[bustub]: https://github.com/cmu-db/bustub