Add a link to Line Length Checker

[peter-kehl]

I like all Markdown Lint checks/features. I love MD013/line-length even more so (because I vary screens, vertical splits, show/hide the navigator/gutter...). So I hoped to find a similar line length checker for other file types, too. And I did find one.

To save other Markdown Lint users' time, please consider adding something like the following to README.md:

If you use `MD013/line-length, you may like SUPERTSY5.line-length-checker-vscode (supertsy5/line-length-checker-vscode). And if you use them together and you want to disable SUPERTSY5.line-length-checker-vscode for Markdown files, have this in your settings.json:

{
...
"line-length-checker.blacklist": [
        "**/*.md"
    ],
...
}

Thank you in advance for considering. Of course, feel free to modify as you see fit.

[nschonni]

Since that extension only has 91 installs, I don't think there are a lot of people running into this

[DavidAnson]

In general, I link to other projects that use this library, but I don't tend to recommend anything else. Prettier gets mentioned a few times because it generates compatibility issues and questions.