repo: Add unconfigured-state to remote config options

This is a migration from the origin version.  It's
nicer to have it in the remote, since that's what one
needs to change.  Then tools don't need to mess with
the origin file.o

In fact in this scenario one can keep the "media source" like
`file:///install/repo` or whatever, since conceptually that's where it
came from.  We're just providing a better error.

Closes: https://github.com/ostreedev/ostree/issues/626

Closes: #627
Approved by: jlebon

man/ostree.repo-config.xml

@@ -179,6 +179,11 @@ Boston, MA 02111-1307, USA.
         <term><varname>tls-ca-path</varname></term>
         <listitem><para>Path to file containing trusted anchors instead of the system CA database.</para></listitem>
       </varlistentry>
+
+      <varlistentry>
+        <term><varname>unconfigured-state</varname></term>
+        <listitem><para>If set, pulls from this remote will fail with the configured text.  This is intended for OS vendors which have a subscription process to access content.</para></listitem>
+      </varlistentry>
     </variablelist>
 
   </refsect1>