Update docs

Build/MQTTnet.nuspec

@@ -15,6 +15,7 @@
 * [Core] Added a builder for application messages using a fluent API
 * [Client] Added a first version of a managed client which will manage the connection, subscription etc. automatically (Thanks to @JTrotta)
 * [Client] The session state response from the server is now returned in the _ConnectAsync_ method and also part of the _Connected_ event args
+* [Client] Added a _TopicFilterBuilder_ using a fluent API (Namespace Changes!)
 * [Server] Added support for WebSockets via ASP.NET Core 2.0 (Thanks to @ChristianRiedl)
 * [Server] Added support for a custom application message interceptor
     </releaseNotes>