add test about yaml comments.

add a xunit test .cs file about yaml comments.
it`s just an easy comment above the property when Serialize(*).

Author: 齐天大胖子

YamlDotNet.Test/Serialization/YamlCommentTests.cs

@@ -0,0 +1,39 @@
+using Xunit;
+using Xunit.Abstractions;
+using YamlDotNet.Serialization;
+
+namespace YamlDotNet.Test.Serialization
+{
+    public class YamlCommentTests
+    {
+        protected readonly ITestOutputHelper Output;
+        public YamlCommentTests(ITestOutputHelper helper)
+        {
+            Output = helper;
+        }
+
+        [Fact]
+        public void SerializationWithComment()
+        {
+            var person = new Person();
+            person.Name = "PandaTea";
+            person.Age = 100;
+            person.Sex = "male";
+
+            Serializer serializer = new Serializer();
+            string result = serializer.Serialize(person);
+
+            Output.WriteLine(result);
+        }
+
+        class Person
+        {
+            [YamlMember(Description = "this is a yaml comment about name property")]
+            public string Name { get; set; }
+            [YamlMember(Description = "this is age")]
+            public int Age { get; set; }
+            [YamlMember(Description = "male or female")]
+            public string Sex { get; set; }
+        }
+    }
+}