Update secure/README.md about the Kerberos component (#401)
Update secure/README.md about the Kerberos component (#401)

to point out the Kerberos optional component is better supported.
dennishuo/dataproc-initialization-actions,GoogleCloudDataproc/initialization-actions,GoogleCloudDataproc/initialization-actions,GoogleCloudDataproc/initialization-actions,dennishuo/dataproc-initialization-actions