man: Add description for mkfs -b option

Describes the block size option -b. This sets the block size, which is
restricted to powers of 2. The linux kernel currently requires that the
block size be equal to the page size to mount.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
1 file changed