Add layout section (tables) to the SPR specification

[rdw-software]

Will do once I've worked with the various effects more.

[Duckwhale]

Completed and published as part of the new docs: https://ragnarokresearchlab.github.io/file-formats/spr/

Edit: Not sure why it's under "Effecs". Maybe I meant STR? If so, that'll come in due time, so closing anyway.