Add new coreos layering example

Author: Michael Burke

post_installation_configuration/coreos-layering.adoc

@@ -56,7 +56,7 @@ RUN rpm-ostree override replace https://example.com/myrepo/haproxy-1.0.16-5.el8.
 
 * *{op-system-base} packages*. You can download {op-system-base-full} packages from the link:https://access.redhat.com/downloads/content/479/ver=/rhel---9/9.1/x86_64/packages[Red Hat Customer Portal], such as chrony, firewalld, and iputils.
 +
-.Example Containerfile to apply a RHEL package
+.Example Containerfile to apply the firewalld utility
 [source,yaml]
 ----
 FROM quay.io/openshift-release-dev/ocp-release@sha256:6499bc69a0707fcad481c3cb73225b867d
@@ -66,6 +66,12 @@ RUN rpm-ostree install firewalld ansible && \
     rpm -e ansible && \
     ostree container commit
 ----
++
+.Example Containerfile to apply the libreswan utility
+[source,yaml]
+----
+include::https://raw.githubusercontent.com/openshift/rhcos-image-layering-examples/master/libreswan/Containerfile[]
+----
 
 * *Third-party packages*. You can download and install RPMs from third-party organizations, such as the following types of packages:
 +
@@ -82,6 +88,14 @@ RUN rpm-ostree install firewalld ansible && \
 ----
 include::https://raw.githubusercontent.com/openshift/rhcos-image-layering-examples/master/htop/Containerfile[]
 ----
++
+.Example Containerfile to apply a third-party package that has {op-system-base} dependencies
+[source,yaml]
+----
+include::https://raw.githubusercontent.com/openshift/rhcos-image-layering-examples/master/fish/Containerfile[]
+----
++
+This Containerfile installs the Linux fish program. Because fish requires additional RHEL packages, the image must be built on an entitled {op-system-base} host.
 
 After you create the machine config, the Machine Config Operator (MCO) performs the following steps: