Documenting read-only rootfs for issue 17927

Issue 17927 (https://github.com/kubernetes/website/issues/17927) asks for a change to this task-focused doc on security-context. It notes that this doesn't mention read-only root filesystem, while it's documented in the PSP page. This adds a bullet for read-only rootfs, clarifies that the bulleted list isn't comprehensive, and tells someone reading the list where to find more. The link is copied from the existing What's Next link list.

content/en/docs/tasks/configure-pod-container/security-context.md

@@ -11,7 +11,7 @@ weight: 80
 {{% capture overview %}}
 
 A security context defines privilege and access control settings for
-a Pod or Container. Security context settings include:
+a Pod or Container. Security context settings include, but are not limited to:
 
 * Discretionary Access Control: Permission to access an object, like a file, is based on
 [user ID (UID) and group ID (GID)](https://wiki.archlinux.org/index.php/users_and_groups).
@@ -28,6 +28,12 @@ a Pod or Container. Security context settings include:
 
 * AllowPrivilegeEscalation: Controls whether a process can gain more privileges than its parent process. This bool directly controls whether the [`no_new_privs`](https://www.kernel.org/doc/Documentation/prctl/no_new_privs.txt) flag gets set on the container process. AllowPrivilegeEscalation is true always when the container is: 1) run as Privileged OR 2) has `CAP_SYS_ADMIN`.
 
+* readOnlyRootFilesystem: Mounts the container's root filesystem as read-only.
+
+The above bullets are not a complete set of security context settings -- please see 
+[SecurityContext](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#securitycontext-v1-core) 
+for a comprehensive list.
+
 For more information about security mechanisms in Linux, see
 [Overview of Linux Kernel Security Features](https://www.linux.com/learn/overview-linux-kernel-security-features)