booting with PXE docs reference "above" and it doesn't exist

[philips]

"root: Use a local filesystem for root instead of one of two in-ram options above"

I don't see anything above on this page: https://coreos.com/os/docs/latest/booting-with-pxe.html

[marineam]

ah, doc for rootfstype got removed at some point. No root= option will default to tmpfs

[philips]

@marineam how should it read? Can you help fix it up?

[philips]

@robszumski @joshix This has to be added to the iPXE docs as well! https://github.com/coreos/docs/blob/master/os/booting-with-ipxe.md

[joshix]

Closed fixed by #796 and #799