Add instructions on setting a volume to read-only

This patch adds a short section on how to set a volume to read-only.

Change-Id: If3658151b84472c552299bd657e946a3b71a2871
Closes-Bug: #1298140

doc/common/section_cli_cinder_manage_volumes.xml

@@ -432,4 +432,5 @@
             </procedure>
         </section>
     </section>
+    <xi:include href="section_cli_cinder_read-only-volumes.xml"/>
 </section>

doc/common/section_cli_cinder_read-only-volumes.xml

@@ -0,0 +1,32 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE section [
+<!ENTITY nbsp "&#160;">
+]>
+<section xmlns="http://docbook.org/ns/docbook"
+    xmlns:xi="http://www.w3.org/2001/XInclude"
+    xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
+    xml:id="cli_read-only-volumes">
+    <title>Set a volume to read-only access</title>
+    <para>To give multiple users shared, secure access to the same
+        data, you can set a volume to read-only access.</para>
+    <para>Run this command to set a volume to read-only access:</para>
+    <screen><prompt>$</prompt> <userinput>cinder read-only-mode-update <replaceable>VOLUME</replaceable> <replaceable>BOOLEAN</replaceable></userinput></screen>
+    <para>Where <replaceable>VOLUME</replaceable> is the ID of the
+        target volume and <replaceable>BOOLEAN</replaceable> is a flag
+        that enables read-only or read/write access to the
+        volume.</para>
+    <para>Valid values for <replaceable>BOOLEAN</replaceable>
+        are:</para>
+    <itemizedlist>
+        <listitem>
+            <para><literal>true</literal>. Sets the read-only flag in
+                the volume. When you attach the volume to an instance,
+                the instance checks for this flag to determine whether
+                to restrict volume access to read-only.</para>
+        </listitem>
+        <listitem>
+            <para><literal>false</literal>. Sets the volume to
+                read/write access.</para>
+        </listitem>
+    </itemizedlist>
+</section>