more docstrings

com.unity.ml-agents/Runtime/Actuators/IDiscreteActionMask.cs

         /// <summary>
         /// Set whether or not the action index for the given branch is allowed.
         /// </summary>
+        /// <remarks>
         /// By default, all discrete actions are allowed.
         /// If isEnabled is false, the agent will not be able to perform the actions passed as argument
         /// at the next decision for the specified action branch. The actionIndex correspond

com.unity.ml-agents/Runtime/Sensors/ISensor.cs

     /// </summary>
     public enum ObservationType
     {
-        // Collected observations are generic.
+        /// <summary>
+        /// Collected observations are generic.
+        /// </summary>
-        // Collected observations contain goal information.
+
+        /// <summary>
+        /// Collected observations contain goal information.
+        /// </summary>
-        // Collected observations contain reward information.
+
+        /// <summary>
+        /// Collected observations contain reward information.
+        /// </summary>
-        // Collected observations are messages from other agents.
+
+        /// <summary>
+        /// Collected observations are messages from other agents.
+        /// </summary>
-
     /// <summary>
     /// Sensor interface for generating observations.
     /// </summary>
-        /// Returns the size of the observations that will be generated.
-        /// For example, a sensor that observes the velocity of a rigid body (in 3D) would return
-        /// new {3}. A sensor that returns an RGB image would return new [] {Height, Width, 3}
+        /// Returns a description of the observations that will be generated by the sensor.
+        /// See <see cref="ObservationSpec"/> for more details, and helper methods to create one.
-        /// <returns>Size of the observations that will be generated.</returns>
-        // TODO OBSOLETE replace with GetObservationSpec.Shape
-        //int[] GetObservationShape();
-
+        /// <returns></returns>
         ObservationSpec GetObservationSpec();
 
         /// <summary>