If you are just wanting to generate documentation from your source code xml comments than DocFx does not require that many new files to be be checked into source control. Sure you will need the basic project structure but all the intermediate / generated files in the output can be excluded from your committed source code using .gitignore files (assuming you are using git).
For example, in these tutorials
You would only really need
- docfx.json
- index.md
- toc.yml
- api/index.md
- api.index.yml
- .gitignore
If you add the following lines to the generated .gitignore from tutorial 1 then all the intermediate and generated documentation yml files will never be committed to git.
api/*.yml
api/.manifest
Hopefully this helps, I know it does not get you 0 extra files like you asked but its a fairly light weight solution to generating api documentation.