improve the xmldocs on call cancellation and disposal

src/csharp/Grpc.Core/AsyncDuplexStreamingCall.cs

@@ -117,6 +117,10 @@ namespace Grpc.Core
         /// Otherwise, requests cancellation of the call which should terminate all pending async operations associated with the call.
         /// As a result, all resources being used by the call should be released eventually.
         /// </summary>
+        /// <remarks>
+        /// Normally, there is no need for you to dispose the call unless you want to utilize the
+        /// "Cancel" semantics of invoking <c>Dispose</c>.
+        /// </remarks>
         public void Dispose()
         {
             disposeAction.Invoke();

src/csharp/Grpc.Core/AsyncServerStreamingCall.cs

@@ -103,6 +103,10 @@ namespace Grpc.Core
         /// Otherwise, requests cancellation of the call which should terminate all pending async operations associated with the call.
         /// As a result, all resources being used by the call should be released eventually.
         /// </summary>
+        /// <remarks>
+        /// Normally, there is no need for you to dispose the call unless you want to utilize the
+        /// "Cancel" semantics of invoking <c>Dispose</c>.
+        /// </remarks>
         public void Dispose()
         {
             disposeAction.Invoke();

src/csharp/Grpc.Core/AsyncUnaryCall.cs

@@ -112,6 +112,10 @@ namespace Grpc.Core
         /// Otherwise, requests cancellation of the call which should terminate all pending async operations associated with the call.
         /// As a result, all resources being used by the call should be released eventually.
         /// </summary>
+        /// <remarks>
+        /// Normally, there is no need for you to dispose the call unless you want to utilize the
+        /// "Cancel" semantics of invoking <c>Dispose</c>.
+        /// </remarks>
         public void Dispose()
         {
             disposeAction.Invoke();

src/csharp/Grpc.Core/CallOptions.cs

@@ -88,7 +88,13 @@ namespace Grpc.Core
         }
 
         /// <summary>
-        /// Token that can be used for cancelling the call.
+        /// Token that can be used for cancelling the call on the client side.
+        /// Cancelling the token will request cancellation
+        /// of the remote call. Best effort will be made to deliver the cancellation
+        /// notification to the server and interaction of the call with the server side
+        /// will be terminated. Unless the call finishes before the cancellation could
+        /// happen (there is an inherent race),
+        /// the call will finish with <c>StatusCode.Cancelled</c> status.
         /// </summary>
         public CancellationToken CancellationToken
         {