Issue #3: Adds some documentation

- Updates the constants module documentation.
- Adds a license file.

LICENSE

@@ -0,0 +1,2 @@
+MIT License
+===========

script/constants_module.py

@@ -1,4 +1,26 @@
-# Module to define several constants used throughout the AV stack
+"""This module defines several constants used throughout the AV stack.
+
+All values are in SI units.
+
+Parameters
+----------
+MAX_ACCELERATION : float
+    The maximum comfortable acceleration the vehicle should experience in
+    normal driving situations. 3.0 [:math:`\\frac{m}{s^2}`]
+MAX_DECELERATION : 9.0 [:math:`\\frac{m}{s^2}`]
+    The maximum deceleration the vehicle should experience when in emergency
+    situations.
+MAX_JERK : 1.3 [:math:`\\frac{m}{s^3}`]
+    The maximum jerk the vehicle should experience in normal driving
+    situations.
+FREEFLOW_SPEED : 1.0 [:math:`\\frac{1}{s}`]
+    The proportional constant when in freeflow driving scenarios (car
+    following).
+MODE_NORMAL : 0
+    Mode representing the vehicle when in normal driving situations.
+MODE_EMERGENCY : 1
+    Mode representing the vehicle when in emergency driving situations.
+"""
 MAX_ACCELERATION = 3.0  # [m/s^2] (positive)
 MAX_DECELERATION = 9.0  # [m/s^2] (positive)
 MAX_JERK = 1.3  # [m/s^3] (positive)