[doc] Issue in "Prerequisites" - Kiwi requirement to be added

[peteingithub]

Prerequisites:

https://documentation.suse.com/suse-edge/3.3/html/edge/quickstart-metal3.html#id-prerequisites

"The SL-Micro.x86_64-6.1-Base-GM.raw OS image file must be downloaded from the SUSE Customer Center or the SUSE Download page."

Would it be Kiwi-created ISO/Raw with 3.3 and later?