Track/trace: upgrade doc
Upgrade the doc based on work being done in Reflow. Lots of notes here: valueflows/vf-app-specs/vf-apps-traversing-the-flows#7. As of now, we did some desk checking on the proposed solution to the bug, and in general the pseudocode for trace. We are hoping that trace code soon to be written will flush out any further issues. Then we can address track, which I'm not sure if Reflow needs.