added xmldocs to ConstantSampler

com.unity.perception/Runtime/Randomization/Samplers/SamplerTypes/ConstantSampler.cs

         /// </summary>
         public float value;
 
+        /// <summary>
+        /// The base seed used to initialize this sampler's state.
+        /// Note that ConstantSamplers do not utilize a baseSeed.
+        /// </summary>
         public uint baseSeed
         {
             get => SamplerUtility.largePrime;
+        /// <summary>
+        /// The current random state of this sampler.
+        /// Note that ConstantSamplers do not utilize a random state.
+        /// </summary>
         public uint state
         {
             get => SamplerUtility.largePrime;
+        /// <summary>
+        /// A range bounding the values generated by this sampler
+        /// </summary>
         public FloatRange range
         {
             get => new FloatRange(value, value);