Updated docs: GPU Post on Linux with AMD cards

[avive]

Reminder to update the docs about linux home smeshers with AMD cards. They must install the amd-pro driver to get Vulkan runtime support. The standard AMD gpu linux drivers don't seem to support Vulkan, at least not on Ubuntu.

[avive]

@AndrewAR2 - is this correct?

[AndrewAR2]

I don't know, but the amd-pro driver supports Vulkan for sure.

[avive]

Test on AMD gpu on Windows 10 and Ubuntu.