Add utt-balance plugin to readme

Author: larose

README.md

@@ -392,9 +392,13 @@ stretched 2013-07-08 08:34 programming
 
 ## Plugins
 
-utt can be extended by installing plugins. Unfortunately, since this
-is a recent feature, no plugins have been listed here yet. Write to
-Mathieu Larose <<mathieu@mathieularose.com>> to add your plugin here.
+`utt` can be extended by installing plugins.
+
+Available plugins:
+
+- [utt-balance](https://github.com/loganthomas/utt-balance) - Adds a balance command that shows worked time against daily and weekly targets
+
+Open an issue or a pull request to add your plugin here.
 
 
 ### Plugin development