[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?

[ranjinimn]

@peteingithub Please let me know the changes I need to make. Do I need to update the content as follows:

A SUSE Linux Micro 6.1 ISO image created using the Kiwi Builder ([Chapter 28, Building Updated SUSE Linux Micro Images with Kiwi](https://documentation.suse.com/suse-edge/3.3/single-html/edge/#guides-kiwi-builder-images))

[peteingithub]

That looks correct. Version 3.4.