README: add video and logo

Signed-off-by: Mikhail Vanyulin <mikhail.vanyulin@rtsoft.de>

board/seco/imx8mm_myon2/README

@@ -38,6 +38,28 @@ https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
 II. Implementation notes
 ========================
 
+Video output and logo
+---------------------
+
+List of supported outputs:
+  * HDMI_1920x1080
+  * RGB_ATM0700D6J
+  * LVDS_ATM0700L61
+  * LVDS_SCF1001C44GGU05
+  * PCONXS
+  * LVDS_AM19201080D1
+  * RGB18_ATM0700D6J
+  * LVDS_G156HAN02.1
+  * GUF_LVDS_SCF1001C44GGU05
+
+The video output is controlled by the "panel" environment variable.
+To select a specific output, set the value to the one of the supported outputs (see above).
+If "panel" is not set, auto detection is performed.
+To disable video output, set the "panel" to "none".
+
+The splash screen image (splash.bmp) is located on the first partition of the boot device,
+and can be easily changed by replacing the file with a new one.
+
 Universal Serial Bus
 --------------------