doc: Make the bit about mib operands a bit clearer
doc: Make the bit about mib operands a bit clearer

Clean up the text about what a mib is.

Signed-off-by: H. Peter Anvin <8a453bad9912ffe59bc0f0b8abe03df9be19379e@zytor.com>

projedi/nasm,techkey/nasm,projedi/nasm,techkey/nasm,projedi/nasm,projedi/nasm,projedi/nasm,techkey/nasm,techkey/nasm,techkey/nasm