How to install rancheros to disk via dhcp, pxe and tftp?

What files do I lay in tftpboot directory ?
what meaning is the following ? boot.sh ?

#!ipxe

Boot a persistent RancherOS to RAM

Location of Kernel/Initrd images

$ set base-url http://releases.rancher.com/os/latest

$ kernel ${base-url}/vmlinuz rancher.state.autoformat=[/dev/sda] rancher.cloud_init.datasources=[‘url:http://example.com/cloud-config’]
$ initrd ${base-url}/initrd
$ boot