Add requirements to README.md

Signed-off-by: Max Fierke <max@maxfierke.com>
Add support paradigm field to Position, preference_level field to Availability

Signed-off-by: Max Fierke <max@maxfierke.com>
Add paradigm validator to Position

Signed-off-by: Max Fierke <max@maxfierke.com>
Add preference_level AR validator to Availability

Signed-off-by: Max Fierke <max@maxfierke.com>
Add user_id and preference_level to allowed params in availability API controller

Signed-off-by: Max Fierke <max@maxfierke.com>
Add description, group_id, and paradigm to position API controller

Signed-off-by: Max Fierke <max@maxfierke.com>