docs(regress): add specific usage content.

Author: wangliang1989

source/module/regress.rst

@@ -82,6 +82,8 @@ regress
     :width: 400 px
     :align: center
 
+.. _-N:
+
 .. _-W:
 
 **-W**\ [**w**]\ [**x**]\ [**y**]\ [**r**]