Show the number of tasks in the default view

[Pelado-Mat]

I needed a simple summary of the tasks listed. Perhaps its usefull for other people.

[rebecca-owen]

Apologies for late reply on this - I like the idea, thanks for the pull request!

I would like to use argparse to make this a bit more robust with multiple options, and I also plan to drop the python2 support. I will aim to do the version work soon - would you be interested in using argparse here? Thanks!