Manpage: Clarify port numbering, fix formatting

debian/ykushcmd.md

@@ -15,6 +15,8 @@ Switchable USB Hub board.
 
 ## Options
 
+Ports numbers start with "1".
+
 **-l**
   ~ List all currently attached YKUSH boards.
 
@@ -33,7 +35,7 @@ Switchable USB Hub board.
 **-s** _serial_
 
   ~ Select the board by serial number. Needed if there's more than
-  one board connected.
+    one board connected.
 
 
 Using "a" as _port_ will affect all ports.