urdl: welcome observers

[rabsef-bicrym]

We have some guests reviewing this repo - if you're reading this, welcome!

SSS was a great pleasure to work with. I have a few thoughts about it:

• I'm excited that I can customize it on my own to my own purposes, to some extent, e.g. slowing down the timing of the call for new data, etc. I think that should stay in.
• I would like it if I had some good examples of utilizing +on-rock to do some work so I could think about those patterns more without it being an effort of first discovery.
• In urdl's application, we are sharing unmodified score information between users about the game being played. This is raw score data consisting of [games-played=@ud [current-streak=@ud max-streak=@ud] [games-won=@ud won-in-one-guess=@ud <...>]]. I considered perhaps reforming that information into a calculated, ordinated list of players in various realms before sending out, or in +on-rock on receiving. It occurs to me that it might be nice, as I have discussed w/ one of the developers of SSS, if I could maybe just kinda automatically do this to the data on receipt. The idea would be something like (a) validate that your score of yourself is the same as the purported canonical score (b) validate that the ranking calculations have been done correctly (one could imagine games of more import where you might feel more compelled to do this - a host shipping around game histories in chess which you could validate yourself, e.g.).