Change description/usage order

[mayrholu]

When calling via command line the help shows usage then description (see official argparse example).
The html-docs show description before usage which may be odd depending on how one uses description.

It would be nice if either the order is changed in general or a flag like :usage_first: existed.

I can open a PR for either one of the solutions if you tell me which one is preferable.

[gaborbernat]

Let's add a flag 👍