Tell which Toornament API requests to make

[Drarig29]

I need to add in the documentation what Toornament API requests to make to get the needed data for this layer.

Stages: https://developer.toornament.com/v2/doc/organizer_stages
Matches: https://developer.toornament.com/v2/doc/organizer_matches

[Drarig29]

For matches, actually I need to use https://developer.toornament.com/v2/doc/organizer_bracket_nodes, which adds the source node of each opponent, so that I can fix Drarig29/brackets-viewer.js#51 and Drarig29/brackets-viewer.js#52.

I should be able to set a position where there is a source_node_id, so that the viewer knows if a participant comes directly from the seeding or comes from a previous match.