Fix trivial copy-paste mistake

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>
Merge pull request #15 from zyga/master

Fix trivial copy-paste mistake
Update usage.rst

This is really great; thanks for putting this package together!

I've got some minor grammatical edits to clarify things a bit.

But on Line 16 I wasn't sure if you can also return a *subclass* of `argparse.ArgumentParser`. Is that also an option?
Merge pull request #17 from deanmalmgren/patch-1

Update usage.rst
Added notes about recent contributions.
Impoved readme.md file formating.
Choices are not always strings - ensure they are strings before joining
Merge pull request #18 from ezralanglois/master

Choices are not always strings - ensure they are strings before joining
New version + add note about alternatives to docs
include subcommand descriptions