change PXE boot order and clean

[GannonTdW]

Once the OS is installed, you have to boot on the disk.
With the opposite, it will always boot on the network

Cf: Issue #685

Changing some of the documentation is good.
Out changing the documentation and the code is better

PS: I don't understand why the part between <del> and </del> is there. So I delete.

[GannonTdW]

I have never learned go and I am not a dev.

Moreover, with this modification, if the network where the PXE server is located is on another network interface (e.g. net1), it will not work.
you would need something like this:

scsi[0-9];net[0-9]