Add Case Studies

[rcya1]

Add documents where we review some of our past robots and go from begin to end of how we iterated on the design / code for that. Some ideas:

• 2020 Shooter (good review of velocity PID)
• 2020 Intake (good review of roller intakes and also servos)
• 2020 Elevator (good review of positional PID)
• 2019 Climb (good review of state machines)
• 2020 Indexer Auto Index (good review of using sensors and state machines)

Add more (TBD)