Add small screencast that demonstrates topydo.

Recorded with ttyrec, processed with tty2gif [1], turned into animated
GIF with ImageMagick and then optimized using ezgif.com [2]

TTY recording also included with this commit.

[1] https://bitbucket.org/antocuni/tty2gif
[2] http://ezgif.com/optimize/8f097380ed.gif

README.md

@@ -18,8 +18,13 @@ are:
 Consult the [wiki][4] for more information about the features and on how to
 use topydo.
 
+[Demo]
+
+![gif][5]
+
 
 [1]: https://github.com/ginatrapani/todo.txt-cli/wiki/The-Todo.txt-Format
 [2]: https://github.com/ginatrapani/todo.txt-cli
 [3]: https://github.com/bram85/todo.txt-tools
 [4]: https://github.com/bram85/topydo/wiki
+[5]: https://raw.githubusercontent.com/bram85/topydo/stable/doc/topydo.gif