point to nfsroot documentation and explain ip parameter

## VPS setup

Some variables need to be passed to the initrd with kernel options. They are

retrieved from `/proc/cmdline`.

retrieved from `/proc/cmdline`. [Here's the official

documentation.](https://github.com/torvalds/linux/blob/master/Documentation/filesystems/nfs/nfsroot.txt)

- `root=/dev/mapper/xvda1_crypt`: The partition that needs to be mounted as root

- `cryptroot=/dev/xvda`: The device that needs to be partitioned and encrypted

- `ip=213.108.110.71::213.108.110.126:255.255.255.128:encrypted-system:eth0:off`

  IP information (

  `<ip>:<??>:<gateway>:<subnet mask>:<hostname>:<network interface>:<???>`)

  IP information:

  `ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>:<dns0-ip>:<dns1-ip>`

### Startup Notification