pre-commit: add `markdownlint` and standardize Markdown files

[jbampton]

Popular tool to standardize a projects Markdown

https://github.com/DavidAnson/markdownlint

Using the CLI with pre-commit:

https://github.com/igorshubovych/markdownlint-cli?tab=readme-ov-file#use-with-pre-commit

So we can have another basic check / hook / test running with pre-commit.

Nice to have standardized and formatted Markdown

So there are about 40+ rules that you can enable/disable and various ways to use ignores

https://github.com/DavidAnson/markdownlint?tab=readme-ov-file#rules--aliases

[dave2wave]

I'll need to investigate this one more deeply.