check inconsistant command in docs/reference/commandline

Signed-off-by: lixiaobing10051267 <li.xiaobing1@zte.com.cn>

docs/reference/commandline/plugin_rm.md

@@ -14,7 +14,7 @@ parent = "smn_cli"
 ```markdown
 Usage:  docker plugin rm [OPTIONS] PLUGIN [PLUGIN...]
 
-Remove a plugin
+Remove one or more plugins
 
 Aliases:
   rm, remove