Miscellaneous sphinx fixes

[kandersolar]

• Closes Broken link in read_midc documentation #1363
• Closes [DOCS] Contributing refers to maintainers, @pvlib/maintainers, but link doesn't work, who are they? #1300
• Closes Documentation: Link to SAM CSV weather file format is broken #1377
• I am familiar with the contributing guidelines
• Tests added
• Updates entries to docs/sphinx/source/api.rst for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels and Milestone are assigned to the Pull Request and linked Issue.

Two things:

1. The README file has this line:

   Please see the Installation page of the documentation for complete instructions.

   It's not broken now, but will be as soon as we release 0.9.1. I guess we should leave that until we're ready to make the next release?

2. The only remaining latest links are in the two markdown files in https://github.com/pvlib/pvlib-python/tree/master/.github. I think it makes sense to leave those as latest.

[kandersolar]

pytest failures are all test_forecast.py #1364

[AdamRJensen]

The ad placement looks good.

[cwhanse]

I'm in favor of merging this. I haven't reviewed all the changes so I won't indicate "approve".

As a side note, I think the "Contributing" page is too long and should be organized into a set of pages. Definitely a different issue.

[kandersolar]

Forgot about this. I'll merge tomorrow unless objections are raised.