Add Zellic Single Pool Audit 2 (#18)

README.md

@@ -76,3 +76,4 @@
 
   - [Zellic Audit (2023-06-21](./spl/ZellicSinglePoolAudit-2023-06-21.pdf)
   - [Neodyme Audit (2023-08-08](./spl/NeodymeSinglePoolAudit-2023-08-08.pdf)
+  - [Zellic Audit (2024-01-02](./spl/ZellicSinglePoolAudit-2024-01-02.pdf)