Running markdown lint on generated README.md

[andys8]

Is this a bug report?

Not really, but a minor improvement

Steps to Reproduce

Create a new elm app

Expected Behavior

Markdown lint won't find issues.
https://github.com/markdownlint/markdownlint
https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint

Actual Behavior

There are 53 issues, but most of them are minor and can easily be fixed.