[mTLS] Update byo-ca.mdx

Author: ngayerie

src/content/docs/ssl/client-certificates/byo-ca.mdx

@@ -98,3 +98,8 @@ If you want to remove a CA that you have previously uploaded, you must first rem
 ```
 
 2. Use the [Delete mTLS certificate endpoint](/api/operations/m-tls-certificate-management-delete-m-tls-certificate) to delete the certificate.
+
+## List the CA hostname associations
+
+You can use the [List Hostname Associations endpoint](/api/operations/client-certificate-for-a-zone-list-hostname-associations) to list the hostname association.
+You'll need to include the query parameter `mtls_certificate_id` where `mtls_certificate_id` is the certificate ID of the uploaded CA.