link to documentation in README broken

[PeerHerholz]

Ahoi hoi there,

Problem:

Trying to get to the documentation through the link in the README leads to a 404, as the link appears to be broken:

The link is https://github.com/nipy/niwidgets/blob/master/nipy.org/niwidgets.

Steps to reproduce:

Clicking on the documentation link in the README.

Possible solution:

Fix the link to lead to the working documentation, which appears to be
https://nipy.org/niwidgets/

Happy to submit a short PR for this in case you want.

Best, Peer

[PeerHerholz]

Just saw that there's an open PR for that here #54.