Railroad diagram for nftable

[egberts]

Need to craft a ruleset for import into a railroad diagram.

Using some online tools like https://www.bottlecaps.de/rr/ui and https://www.bottlecaps.de/convert/ and a bit of manual fixes we can have a nice navigable railroad diagram.

Copy and paste the EBNF (to be supplied by this issue) on https://www.bottlecaps.de/rr/ui on the tab Edit Grammar the click on the tab View Diagram to see/download a navigable railroad diagram.

Somehow make the railroad diagram part of nftable documentation over at https://wiki.nftables.org/wiki-nftables/index.php/Main_Page