Centos Stream and ultimately RHEL have switched to asynchronous
device initialization, which impacts root device hints and their
usability on those systems, in large part because context which
people have traditionally had, no longer holds true on those newer
kernels.
This doc update attempts to provide the needful context to guide
operators to the best possible outcome given the distribution changes.
Change-Id: I541086cfe235b10f1f1dba95fad95022a22f9ce7
ac31720ac1