docs: add page describing the libvirt daemons

Now that we have more than just the libvirtd daemon, we should be
explaining to users what they are all for & important aspects of their
configuration.
Reviewed-by: NErik Skultety <eskultet@redhat.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

docs/docs.html.in

@@ -18,6 +18,9 @@
         <dt><a href="migration.html">Migration</a></dt>
         <dd>Migrating guests between machines</dd>
 
+        <dt><a href="daemons.html">Daemons</a></dt>
+        <dd>Overview of the daemons provided by libvirt</dd>
+
         <dt><a href="remote.html">Remote access</a></dt>
         <dd>Enable remote access over TCP</dd>