Enable auto pdf generation

[matmaxgeds]

I think this should just be a config tweak? https://readthedocs.org/projects/docs/downloads/pdf/latest/#section.2.5

Inspired by Rolf here: IATI#15

[andylolz]

I think this should just be a config tweak

Yep, I think you are right!

[andylolz]

@matmaxgeds I’ve had a go at pushing to readthedocs.io here:
https://iati-standard.readthedocs.io

The auto-generated PDF is 4 pretty much blank pages! So something isn’t quite working there.

Other thoughts on using readthedocs.io:

• Pros: You get a few nice features out of the box, e.g. revision SHA in the footer; different versions built from different branches; PDF (although not quite working for us yet) etc. We could probably get these things working on github pages, but it probably requires a bit more wrangling with sphinx config.
• It’s easy to add a custom domain, so we could easily host it at: https://reference.codeforiati.org
• Cons: It’s not as fast as github pages, and there are adverts