Update docs.

Build/MQTTnet.nuspec

@@ -23,6 +23,7 @@
 * [Server] Exposed _ClientCertificateRequired_ and _CheckCertificateRevocation_ at TLS options.
 * [Server] Exposed client certificate at client connection validator.
 * [Server] The subscription interceptor now supports altering the entire topic filter.
+* [MQTTnet.Server] Added authentication support via Python script file.
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2019</copyright>
     <tags>MQTT Message Queue Telemetry Transport MQTTClient MQTTServer Server MQTTBroker Broker NETStandard IoT InternetOfThings Messaging Hardware Arduino Sensor Actuator M2M ESP Smart Home Cities Automation Xamarin</tags>