f2fs: add description for fsck.f2fs and dump.f2fs

This patch adds some description on fsck.f2fs and dump.f2fs which is
recently merged into f2fs-tools.

Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
1 file changed