Use sphinx opengraph

[ericholscher]

This makes social previews for the site automatically really pretty:

https://github.com/wpilibsuite/sphinxext-opengraph

It should just be an "install and forgot" option, but it would make this tweet look nicer :)

https://twitter.com/readthedocs/status/1628814555420979200

[ketozhang]

Lack of OpenGraph also affects RSS readers. Here Feedly,

[ketozhang]

@evildmp @vmagnin I've submitted a small PR to address this. Appreciate it if you have a few minutes to take a look.

[vmagnin]

@ketozhang
I am not familiar with Sphinx. All I can say about the PR #77 is that the screenshots look good. As a user of Diataxis, I immediately identify it in these three screenshots.