🚀 Feature: Lint for missing relative links in Markdown files

[JoshuaKGoldberg]

Bug Report Checklist

• I have tried restarting my IDE and the issue persists.
• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

I just discovered the hard way that the README.md contains an incorrect path for a relative link 😱:

create-typescript-app/README.md

Line 48 in 30ea110

- [Migrating an existing repository](./docs/Migrate.md): adding this template's tooling on top of an existing repository

(the file name is Migration.md, not Migrate.md)

That kind of typo should have been caught in CI. Surely there's some lint rule somewhere that could do this?

Additional Info

I did a quick Google and found https://github.com/theoludwig/markdownlint-rule-relative-links. Maybe that's usable?

If we end up switching to eslint-plugin-mdx or some such (#567), we'd want a lint rule from that config/plugin.

[Paulie-Aditya]

why don't we just change the docs to say ./docs/Migration.md ?

[JoshuaKGoldberg]

Not sure what you mean there. This issue is for adding tooling that will automatically find incorrect links, not about any specific incorrect link that exists today.