Add github action file

[errnesto]

I think this is all you need to create a github action out of this.

As an alternative it would be possible to list all the arguments as github action arguments…
But doing it like this, it's easier to keep the action up to date and we keep the same interface which is already documented.

I created the action here: https://github.com/wunderundfitzig/linkcheck-action because I need to use it in a project.
I'm happy to hand over the repository if it would be better to keep the action in a seperate repo.
I would depricate that repo if a official action exists :-)

I guess this closes #46

[filiph]

Sorry this took so long. I hoped to have time to take a closer look at GitHub Actions but, to be completely honest, I don't think I'll have the time anytime soon. This change looks good, so I'm merging.

Thank you for the contribution! Please let me know if it works on your end.

[filiph]

Ok, follow up question. Here's what github tells me about the action:

What's a good naming convention for such an action?

[errnesto]

Hm I don't really know any naming conventions… all I can do is copy what they write here (https://docs.github.com/en/actions/creating-actions/publishing-actions-in-github-marketplace) :-)

The name in the action's metadata file must be unique.

• The name cannot match an existing action name published on GitHub Marketplace.
• The name cannot match a user or organization on GitHub, unless the user or organization owner is publishing the action. For example, only the GitHub organization can publish an action named github.
• The name cannot match an existing GitHub Marketplace category.
• GitHub reserves the names of GitHub features.

So I guess linkcheck is taken by some user or organisation… I delisted my version of your action so maybe linkcheck-action will work now?