Added 0.7.3 release information to the changelog

Author: westei

docs/src/changelog.asciidoc

@@ -5,6 +5,15 @@
 
 This document shows the changes that are introduced into Smarti with the releases.
 
+== Smarti 0.7.3 Release Notes
+May 15^th^, 2018
+
+Smarti `0.7.3` contains a fix to the Chatpal Backend
+
+=== New in Smarti 0.7.3
+
+* https://github.com/redlink-gmbh/smarti/issues/249[#249 - CloudSync does not work for deleted Conversations]
+
 == Smarti 0.7.2 Release Notes
 May 14^th^, 2018