Update MQTTnet.nuspec

Update docs.

Build/MQTTnet.nuspec

@@ -12,7 +12,8 @@
     <requireLicenseAcceptance>true</requireLicenseAcceptance>
     <description>MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker) and supports v3.1.0, v3.1.1 and v5.0.0 of the MQTT protocol.</description>
     <releaseNotes>
-* [Core] Removed IDisposable from MqttClientConnection.cs (Fixes #1284).
+* [Core] Removed IDisposable from MqttClientConnection.cs (#1284).
+* [Server] Improved session management for MQTT v5 (#1294, thanks to @logicaloud).
 Git commit: $gitCommit
     </releaseNotes>
     <copyright>Copyright Christian Kratky 2016-2021</copyright>