explain BDS and the custom CONFIG_EFI_BDS patch etc

[orangecms]

The website and also https://github.com/linuxboot/linuxboot are referring to a CONFIG_EFI_BDS option that was once based on a custom patch; see also: linuxboot/linuxboot#96

OTOH, https://github.com/linuxboot/book/blob/main/src/implementation.md explains steps to implement LinuxBoot on top of a vendor provided UEFI PI, which also involves BDS, but pictures a different approach again. People looking for details would get lost here.
We need to elaborate on the whole thing.