docs(pkg/certificate/README.md): fix broken document link
This package contains tools for issuing and renewing certificates for the service mesh.
-For design and details on mTLS and certificate issuance please see [docs/patterns/certificates.md](../../docs/patterns/certificates.md).
+For design and details on mTLS and certificate issuance please see [docs/patterns/certificates.md](../../docs/certificate_management.md).
## Interfaces
