Add site_url

[Shrinks99]

Changes

• Tells MkDocs where the site will be published at allowing it to generate a sitemap

[ikreymer]

This should probably be parametrized, since local deployment will have the docs hosted locally at: http://localhost:30870/docs/ or a local domain...

[Shrinks99]

I don't think it does much that would affect the local builds? The value is ignored for the locally built sitemap with mkdocs serve

Details here: https://www.mkdocs.org/user-guide/configuration/#site_url

...That said you're also not wrong! What would be the best way of making this variable? Could add a line that appends it to the docs deploy script?