add preview functionality to PRs

[egpbos]

Currently, contributors (and reviewers) are advised to spin up a webserver locally to check out whether their changes render properly. Obviously, nobody does this. I have seen other repos automatically spin up a netlify or similar free server to create a preview of the website and link to it in the PR. For the Guide, I think this could be done even simpler, because the Guide is static content, it doesn't need a complicated webserver. Anybody have ideas of how to make this happen? I think it would greatly smoothen the contribution process and improve reviews (surely my own, because I'm only now noticing rendering errors in #328 😉).

[sverhoeven]

I setup netlify for PRs in one of my repos see for example i-VRESSE/workflow-builder#169 . I am using the Open Source team plan. Bad thing about Netlify is that they do not have bandwidth or build time limits, they will charge you if you go over your plan limit. So maybe another service is better.

[egpbos]

Maybe we can use this? https://github.com/rossjrw/pr-preview-action

[bouweandela]

I looked into that one, but my impression is that it commits all the previews to your default git branch, which doesn't seem desirable to me.