updated xml docs

com.unity.perception/Runtime/Randomization/Samplers/SamplerState.cs

 namespace UnityEngine.Experimental.Perception.Randomization.Samplers
 {
+    /// <summary>
+    /// Encapsulates the random state that all samplers mutate when generating random values
+    /// </summary>
     public static class SamplerState
     {
         /// <summary>