Add renaming advice based on Linux kernel spelling (#1554)

Recommend the renaming of whitelist/blacklist to allowlist/blocklist as
per kernel patch:
https://lore.kernel.org/lkml/20200609122549.26304-1-sjpark@amazon.com/

“[T]he new suggestions are incontrovertible, doesn't make people hurt,
 and more self-explanatory.”