move website related sphinx content to separate repo

[fzahle]

to simplify things for users I think we should separate the website related sphinx content, i.e. index, news to another repo and keep the fusedwind sphinx docs as minimalist as possible conforming to openmdao's plugin build_docs fused wind and use a more minimal theme, rather than forcing users to download a bunch of extra sphinx dependencies.

building the website should then have a procedure to pull the fusedwind .rst files and build them with the website theme.

see https://github.com/ipython for inspiration.

we don't need to be in a rush to do this, but as our website grows it would be nice to keep the two things separate.