Added a section on how to flash an SD card (wic) image to the eMMC memory on BL i.MX8MM using dd.

Some customers who received or bought a BL i.MX8MM had no OS on the internal eMMC memory and right now there is now step by step guide on how to transfer a wic image to the eMMC. This part of the Getting Started Guide is intended to fill this gap, at least in part, as not everything that is involved is explained like UBoot. But it will help those who want to boot off eMMC and have the right BootConfiguration.