[Feat]: Explain the pairing algorithm

[KingSupernova31]

There are multiple possible generalizations of Swiss pairings to multiplayer, so it's non-obvious how SquireBot does it. Given the importance of this algorithm to players and tournament organizers (determines the best way to structure prizes, and when a player should drop or draw), I think it'd be worth having a brief explanation available somewhere for those who are interested, even if just as a reply to this issue.

(Bringing this up because I'm making a tournament math simulator for players and TOs to use, and I'd like it to support SquireBot multiplayer tournaments.)