Documentation: Relative Trip Scheduling

[dhensle]

The following addition to models.rst explaining the relative trip scheduling logic seems to have gotten lost as I do not see it anywhere in the new documentation...?

https://github.com/ActivitySim/activitysim/pull/657/files#diff-d606c1bcd72689c8bb949dcdafe4bcd0420da5cbaa7daf9614f0757734cffaf7

[jpn--]

That documentation now lives in the trip scheduling component documentation here:

activitysim/docs/dev-guide/components/trip_scheduling_probabilistic.md

Lines 26 to 34 in 2f9afa0

	In order to avoid trip failing, a new probabilistic trip scheduling mode was developed named "relative".
	When setting the _scheduling_mode_ option to relative, trips are scheduled relative to the previously scheduled trips.
	The first trip still departs when the tour starts and for every subsequent trip, the choices are selected with respect to
	the previous trip depart time. Inbound trips are no longer handled in reverse order. The key to this relative mode is to
	index the probabilities based on how much time is remaining on the tour. For tours that include subtours, the time remaining will
	be based on the subtour start time for outbound trips and will resume again for inbound trips after the subtour ends.
	By indexing the probabilities based on time remaining and scheduling relative to the previous trip, scheduling trips in relative
	mode will not fail. Note also that relative scheduling mode requires the use of logic
	version 2 (see warning about logic versions, below).