Set up GitHub pages and link to Sphinx documentation

[Sebanisu]

Might need to move the docs folder to a raw_docs or raw/docs.

Because github pages kinda only can look at the docs folder or the root folder.

You need to copy the generated html into the new docs folder.

Add an empty file named .nojekyll this is because you aren't using jekyll.

How best to automate this? I'm not sure.

[Sebanisu]

You could always change set(SPHINX_BUILD ${CMAKE_CURRENT_BINARY_DIR}/sphinx) to set(SPHINX_BUILD ${PROJECT_SOURCE_DIR}/docs) then when you build the docs it'd update the folder and you just need to commit the changes.