updated xml docs

com.unity.perception/Runtime/Randomization/Randomizers/RandomizerExamples/Randomizers/BackgroundObjectPlacementRandomizer.cs

         GameObject m_Container;
         GameObjectOneWayCache m_GameObjectOneWayCache;
 
+        /// <inheritdoc/>
         protected override void OnCreate()
         {
             m_Container = new GameObject("BackgroundContainer");

com.unity.perception/Runtime/Randomization/Randomizers/RandomizerExamples/Randomizers/ForegroundObjectPlacementRandomizer.cs

         GameObject m_Container;
         GameObjectOneWayCache m_GameObjectOneWayCache;
 
+        /// <inheritdoc/>
         protected override void OnCreate()
         {
             m_Container = new GameObject("Foreground Objects");

com.unity.perception/Runtime/Randomization/Randomizers/RandomizerTagManager.cs

     /// </summary>
     public class RandomizerTagManager
     {
+        /// <summary>
+        /// Returns the singleton RandomizerTagManager instance
+        /// </summary>
         public static RandomizerTagManager singleton { get; } = new RandomizerTagManager();
 
         Dictionary<Type, HashSet<Type>> m_TypeTree = new Dictionary<Type, HashSet<Type>>();