erofs-utils: update README

Make it easier to understand...

Link: https://lore.kernel.org/r/20201121022623.3882-2-hsiangkao@aol.com
Reviewed-by: Li Guifu <bluce.lee@aliyun.com>
Signed-off-by: Gao Xiang <hsiangkao@aol.com>
1 file changed