The alternative small firmware needs a few words of what it can and
absolutely cannot do; this adds those words.

Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20220506055124.3822112-1-aik@ozlabs.ru>
[danielhb: added linebreaks before and after table]
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>