imx8mq_evk/README: add missing firmware extract step

Tested-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
diff --git a/board/freescale/imx8mq_evk/README b/board/freescale/imx8mq_evk/README
index 1da6eaf..004fa3f 100644
--- a/board/freescale/imx8mq_evk/README
+++ b/board/freescale/imx8mq_evk/README
@@ -18,6 +18,7 @@
 Note: srctree is U-Boot source directory
 $ wget https://www.nxp.com/lgfiles/NMG/MAD/YOCTO/firmware-imx-7.9.bin
 $ chmod +x firmware-imx-7.9.bin
+$ ./firmware-imx-7.9.bin
 $ cp firmware-imx-7.9/firmware/hdmi/cadence/signed_hdmi_imx8m.bin $(srctree)
 $ cp firmware-imx-7.9/firmware-imx-7.9/firmware/ddr/synopsys/lpddr4*.bin $(srctee)