Broken links on Data & Methods page

[capnrefsmmat]

All three links in the first paragraph of the Data & Methods page are broken, because they write https:/ instead of https://. The first link under the "About Our Methodology" heading has the same problem.

(might be worth using grep to check all the markdown files in case I missed some)

[capnrefsmmat]

Looks like this happens in a couple places on the About page linking to the API docs too