Updating the versioning in relation to the plugin system

Author: joseph-flinn

CHANGES

@@ -4,6 +4,14 @@ Changelog
 
 Here you can find the recent changes to tmuxp
 
+tmxup 1.5.8 (2020-09-*)
+-----------------------
+- :issue:`530` Add plugin system for user customization of tmuxp
+- :issue:`530` Add tests for the plugin system
+- :issue:`530` Update existing tests for the plugin system
+- :issue:`530` Add the plugin interface to the tmuxp package
+- :issue:`530` Add in depth documentation for the plugin system
+
 current
 -------
 - *Insert changes/features/fixes for next release here*