Broken link to tutorial on https://contributing.shields.io/index.html

Are you experiencing an issue with...

- [x] [shields.io] https://contributing.shields.io/index.html

:beetle: **Description**
The link for `tutorial on how to add a badge.` appears to be broken on the site deployed to `contributing.shields.io`. The link is pointing to `https://contributing.shields.io/doc/TUTORIAL.md` which does not exists. The source on `https://github.com/badges/shields/blob/master/README.md` works though and it links to `https://github.com/badges/shields/blob/master/doc/TUTORIAL.md`. It looks like the same content is deployed at `https://contributing.shields.io/tutorial-tutorial`

:bulb: **Possible Solution**

Inspect the tutorial link in README.md and the deployed page at contributing.shields.io/index.html, then compare it with doc/TUTORIAL.md and the reported tutorial-tutorial location. Done means the tutorial link on the deployed site resolves to the intended tutorial content.

Written by the indexing model from the issue text.