imx6ulpico/readme: Update the image layout file

As we are using the common image layout now, update the
readme.txt file accordingly.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/technexion/imx6ulpico/readme.txt

@@ -46,7 +46,7 @@ command as root:
 *** WARNING! This will destroy all the card content. Use with care! ***
 
 For details about the medium image layout, see the definition in
-board/technexion/imx6ulpico/genimage.cfg.
+board/freescale/common/genimage.cfg.template.
 
 Boot the i.MX6UL Pico board
 =========================