Merge pull request #44527 from jldohmann/OSDOCS-3328

OSDOCS-3328: add kerberos extension

Author: jeana-redhat

modules/rhcos-add-extensions.adoc

@@ -8,10 +8,12 @@
 = Adding extensions to {op-system}
 {op-system} is a minimal container-oriented RHEL operating system, designed to provide a common set of capabilities to {product-title} clusters across all platforms. While adding software packages to {op-system} systems is generally discouraged, the MCO provides an `extensions` feature you can use to add a minimal set of features to {op-system} nodes.
 
-Currently, the following extension is available:
+Currently, the following extensions are available:
 
 * **usbguard**: Adding the `usbguard` extension protects {op-system} systems from attacks from intrusive USB devices. See link:https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html-single/security_hardening/index#usbguard_protecting-systems-against-intrusive-usb-devices[USBGuard] for details.
 
+* **kerberos**: Adding the `kerberos` extension provides a mechanism that allows both users and machines to identify themselves to the network to receive defined, limited access to the areas and services that an administrator has configured. See link:https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/system-level_authentication_guide/using_kerberos[Using Kerberos] for details, including how to set up a Kerberos client and mount a Kerberized NFS share.
+
 The following procedure describes how to use a machine config to add one or more extensions to your {op-system} nodes.
 
 .Prerequisites