token-2022: Add Certora audit report (#22)

README.md

@@ -73,6 +73,7 @@
   - [OtterSec Audit (2023-11-03).pdf](./spl/OtterSecToken2022Audit-2023-11-03.pdf)
   - [OtterSec ZK Token SDK Audit (2023-11-04).pdf](./spl/OtterSecZkTokenSdkAudit-2023-11-04.pdf)
   - [Halborn Audit (2024-03-08).pdf](./spl/HalbornToken2022Audit-2024-03-08.pdf)
+  - [Certora Audit (2024-05-24).pdf](./spl/CertoraToken2022Audit-2024-05-24.pdf)
 
 ### Account Compression