Put docs on readthedocs

[keflavich]

To include in the frontpage:

• a timeline for inclusion in astropy core (>=3 months, but the goal is to have it in core)
• correctness comparison to pyregion
• speed comparison to pyregion

[keflavich]

@joleroi you should be able to start the readthedocs package from this URL:
https://readthedocs.org/dashboard/import/?
though... I'm not seeing it there...

[joleroi]

I put a minimal docs page on rtd.

http://astropy-regions.readthedocs.org/en/latest/

[cdeil]

@keflavich - I'm closing this issue, since the title says "put docs on readthedocs" and they are up.

Concerning the other tasks you list above:

• I don't think we can give a timeline for inclusion in the astropy core ... we don't know when someone will work on this and when it will be ready.
• Concerning comparison to pyregion, I'll make a separate issue.