FYI: secondary sampling design

[Adrian Cole]

Hi, all

Just wanted to let you know, I've posted a wiki with secondary
sampling design here:
https://github.com/openzipkin/openzipkin.github.io/wiki/secondary-sampling#goal

This is something Nara and I had worked on, and was reviewed in some
forms on a brave pull request here:
https://github.com/openzipkin/brave/pull/958

I've asked Bas to help with the design side of things, too, but
everyone is welcome. I just don't want to be busfactor 1 on this, heh.

Anyway, enjoy!
-A