Contributing guide on github.io still has a broken link to the CMake Options

[ericniebler]

If you navigate to Submitting a PR / Configure CMake Builds, you'll find a broken link to "CMake Options". The URL points to:

https://nvidia.github.io/thrust/contributing/setup/cmake_options.md

There are two things wrong with this URL:

1. It is linking to a .md file and it should be linking to a .html file.
2. The cmake_options.html file doesn't live at thrust/contributing/setup/cmake_options.html. It lives at thrust/setup/cmake_options.html.

(#​2) could be explained if the docs on nvidia.github.io/thrust haven't been republished since NVIDIA/thrust#1639 was merged. In that PR, @brycelelbach claims that URLs ending with .md should auto-magically be rewritten as .html, but clearly that isn't happening.

[alliepiper]

Blocked as we'll need to update this as part of the monorepo update anyway, so we'll address this after the repo merge.