README.md: add screencast, closes #128

Author: mykter

README.md

@@ -15,6 +15,9 @@ To determine how you spend your time, TagTime literally randomly samples you. At
 
 See http://messymatters.com/tagtime for the whole story.
 
+Here's a clip of an intrepid user getting pinged by TagTime whilst job hunting. As well as what "project" they're working on, they're also using TagTime to record what tools they're using - in this case, emails. Later, they'll be able to analyze their tags to see how they spend their time on the computer.
+![cast](https://user-images.githubusercontent.com/1424497/38167805-653e89fc-3534-11e8-9b41-cedae5ff2e62.gif)
+
 Inspired by [alice0meta](https://github.com/alice0meta/TagTime).
 
 # Installation and Quick Start