Update breaking chnages note with info about custom serialization settings.

Hello Guys,

Looks like folks are confused how to change default serialization settings in NEST 2.x.

I've added little help, hope you are gonna like it :)

Author: robertlyson

docs/2.0-breaking-changes/nest-breaking-changes.md

@@ -205,6 +205,42 @@ public class StringTimeSpanConverter : JsonConverter
 }
 ```
 
+#Serialization settings
+
+Serialization settings are now configurable through `ConnectionSettings` constructor and are stored in one single class.
+
+
+```c#
+var setting = new ConnectionSettings(..);
+
+setting.AddContractJsonConverters(type => new MyPrettyConverter(), type => new SomeOtherConverter());
+setting.SetJsonSerializerSettingsModifier(settings => settings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore);
+```
+
+becomes
+
+```c#
+var settings = new ConnectionSettings(connectionPool, connectionSettings => new MyJsonNetSerializer(connectionSettings))
+
+public class MyJsonNetSerializer : JsonNetSerializer
+{
+	public MyJsonNetSerializer(IConnectionSettingsValues settings) : base(settings)
+	{
+	}
+
+	protected override void ModifyJsonSerializerSettings(JsonSerializerSettings settings)
+	{
+		settings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;
+	}
+
+	protected override IList<Func<Type, JsonConverter>> ContractConverters => 
+		new List<Func<Type, JsonConverter>>
+		{
+			type => new MyPrettyConverter(),
+			type => new SomeOtherConverter()
+		};
+}
+```
 
 #Renamed Types