[PATCH] libertas: updated readme file

Fix some wording and blinding table command options, clarify argument list for
fwt_add and fwt_list, simplify fwt_list_route

Signed-off-by: Luis Carlos Cobo Rus <luisca@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>