docs: add full workflow description of how race result import works

[louking]

• results are imported to managedresult table
• edit participants is used to pick and choose results for which the names aren't exactly matched
  • options are given for each matching runner who was a "member" on the race date (including grace period)
  • runner records which are not in the window between Renewal (minus grace period) and Expiration dates are ignored
• tabulate takes accepted results and puts into the raceresult table
• standings uses results from the raceresult table