UP Squared 6000: describe how to install an image on the eMMC storage

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

content/reference_hardware/upsquared6000_setup.md

@@ -57,6 +57,18 @@ picocom /dev/ttyUSB0 -b 115200
 ```
 5. Plug in the power supply and wait for it to boot.
 
+{{% notice note %}}
+Using USB is the easiest way to boot the board, however for testing and
+production enviroments it is recommended to install Apertis images on the eMMC.
+In order to do it, start the board with a system from a USB device as described
+above, and then install your image on the eMMC storage of the board with:
+```
+sudo bmaptool copy path/to/image.img.gz /dev/mmcblk0
+```
+Please note that the path given as an argument here should contain both
+`image.img.gz` and `image.img.bmap` in order to take advantage of bmaptool.
+{{% /notice %}}
+
 ## Serial console
 
 The 10-pin header adapter from the [up-shop](https://up-shop.org/usb-2-0-pin-header-cable.html)