Provide a link to the Sphinx documentation about using a theme

[choldgraf]

I suspect that many people landing on this website will be new to the Sphinx ecosystem, and will be trying to find a theme that works with their documentation. For many, it may be unclear how to set a new theme in the Sphinx configuration and this is the first site they land on. It would be helpful if there were a link somewhere on the website that said something like "For information about how to configure Sphinx to use a theme, see the Sphinx theming documentation"

[pradyunsg]

This is now covered by "quickstart" in the theme sample sites, which clearly lays out the steps for how to use the theme.

[pradyunsg]

https://sphinx-themes.org/sample-sites/sphinx-rtd-theme/quickstart/

Should've included a link!