Modifying the documentation

docs/Python-API.md

 
 A `BehaviorSpec` has the following fields :
 
-- `observation_shapes` is a List of Tuples of int : Each Tuple corresponds to an
-  observation's dimensions (without the number of agents dimension). The shape
-  tuples have the same ordering as the ordering of the DecisionSteps,
+- `sensor_spec` is a List of `SensorSpec` objects : Each `SensorSpec`
+  corresponds to an observation's properties: `shape` is a tuple of ints that
+  corresponds to the shape of the observation (without the number of agents dimension).
+  `dimension_property` is a tuple of flags containing extra information about how the
+  data should be processed in the corresponding dimension. Note that the `SensorSpec`
+  have the same ordering as the ordering of observations in the DecisionSteps,
   DecisionStep, TerminalSteps and TerminalStep.
 - `action_spec` is an `ActionSpec` namedtuple that defines the number and types
   of actions for the Agent.