Short list of rules - in case they are helpful

[clach04]

Check out https://github.com/too-much-todotxt/spec/wiki/Short-Rules

NOTE 4 and 6 might be considered controversial (too-much-todotxt/spec#15) - one could always change the shortlist to match the https://github.com/todotxt/todo.txt/blob/master/README.md spec