如何創建基於arm 的Ubuntu rootfs

參考：

• https://blog.csdn.net/u010632165/article/details/78424000
• https://www.jianshu.com/p/7453d52f0324
• https://blog.csdn.net/sinat_37141443/article/details/80882219
• https://www.cnblogs.com/pengdonglin137/p/9540670.html
• https://blog.csdn.net/zpcindy/article/details/79983835