docs(misc/contribute): make anchor links work properly

[caitp]

The hash links in misc/contribute were never going to hit the right target, and would cause a
404 (which, by the way, causes over 1000 errors in the console, it would be good to look into
those!).

This probably isn't the best solution for this, but it works for now, so that's nice.

[mary-poppins]

Thanks for the PR! Please check the items below to help us merge this faster. See the contributing docs for more information.

• Uses the issue template (#6706)

If you need to make changes to your pull request, you can update the commit with git commit --amend.
Then, update the pull request with git push -f.

Thanks again for your help!