docs: formatdomain: Mention missing protocols

http, https, ftp, ftps, and tftp were not mentioned in the
documentation. Note that 'ssh' is still omitted as it's used only
internally.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

docs/formatdomain.html.in

@@ -3096,10 +3096,11 @@
               <dd>
               The <code>protocol</code> attribute specifies the protocol to
               access to the requested image. Possible values are "nbd",
-              "iscsi", "rbd", "sheepdog", "gluster" or "vxhs".
+              "iscsi", "rbd", "sheepdog", "gluster", "vxhs", "http", "https",
+              "ftp", ftps", or "tftp".
 
-              <p>If the <code>protocol</code> attribute is "rbd", "sheepdog",
-              "gluster", or "vxhs", an additional attribute <code>name</code>
+              <p>For any <code>protocol</code> other than <code>nbd</code>
+              an additional attribute <code>name</code>
               is mandatory to specify which volume/image will be used.
               </p>