Merge "Added note to os_command_line"

doc/cli-reference/ch_cli_glance_property_keys.xml

@@ -282,7 +282,8 @@
                 <td>os_command_line</td>
                 <td>The kernel command line to be used by the libvirt driver, instead of the
                     default. For linux containers (LXC), the value is used as arguments for
-                    initialization.</td>
+                    initialization. This key is valid only for Amazon kernel, ramdisk,
+                    or machine images (aki, ari, or ami).</td>
                 <td/>
             </tr>
             <tr valign="top">