Guidelines for Adding New Plans

[hjsuh94]

NOTE: This issue will be migrated to README.
Documenting all the steps one needs to take to add a new plan.

1. Write new plan files new_plan.cc and new_plan.h.
2. Make sure to add them to the cmake file for plans.
3. Make a new MakeNewPlan method of IiwaPlanFactory (define them in both iiwa_plan_factory.cc and iiwa_plan_factory.h that takes care of how plans are handled from plan lcm messages.

[pangtao22]

We should also consider using custom LCM types for our plans. Right now plan types are determined by the first string field in robot_state.name, which is going to get messy as we support more plans.

[pangtao22]

If the new Plan needs additional LCM subscriptions: #42