github中的README.md快速布局和换行

这样的文字：

Usage: mkheader -l image

-l ==> list image header information

mkheader [-x] -A arch -O os -T type -C comp -a addr -e ep -n name -d data_file[:data_file...] image

-A ==> set architecture to 'arch'

-O ==> set operating system to 'os'

-T ==> set image type to 'type'

-C ==> set compression type 'comp'

-a ==> set load address to 'addr' (hex) 30008000

-e ==> set burn address to 'addr' (hex) bootloader->0x0 kernel->0x60000 rootfs->0x560000

-n ==> set image type bootloader->'BOOT' kernel->'KERN' rootfs->'ROOT'

-d ==> use image data from 'datafile'

-x ==> set XIP (execute in place)

直接显示是这样的：