Become a SunPy affiliated package

[namurphy]

Here's the process. There's a new partnership between SunPy and pyOpenSci so the review process may have changed.

[Cadair]

We haven't formalised anything with pyopensci yet, so no change.

As I am doing the joss review, I will be able to pretty speedily go over the sunpy affiliated package review as well, so once the joss stuff is wrapped up please add yourselves to the sunpy affiliated list!!

[joyvelasquez]

This process is currently in the works: Affiliated Package Review Request: XRTpy #431, sunpy/sunpy.org#431.