Add sitemap generator to website for crawling.

[sbryngelson]

Description

I'm not sure if it works. It seems like it should.

Fixes #349

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)

Scope

• [x] This PR comprises a set of related changes with a common goal

If you cannot check the above box, please split your PR into multiple PRs that each have a common goal.

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• It hasn't been tested because I'm not entirely sure how to do so locally.

[sbryngelson]

@henryleberre would be glad to have your review here.