Add note about having explicit serviceAccountName

Author: sebrandon1

modules/cnf-best-practices-automount-services-for-pods.adoc

@@ -14,5 +14,7 @@ spec:
   automountServiceAccountToken: false
 ----
 
+Pods must include an explicit `serviceAccountName` in the pod spec. This is required to ensure that the pod is not automatically assigned the default service account.
+
 See test case link:https://github.com/test-network-function/cnf-certification-test/blob/main/CATALOG.md#access-control-pod-automount-service-account-token[access-control-pod-automount-service-account-token]