Add PR previews - Githubissues

I made an Action for generating previews of pull requests. I've been having trouble with testing #8 (localhost doesn't want to talk to Crom/Wikidot for some reason, even when running a server), and don't much fancy uploading files to Wikidot every time I change something. So I'm hoping that deploying tests to Pages and pulling from there will be easier - plus, it has the following advantages:

everyone on the tech team can instantly see changes
if it doesn't work, then we'll know that our plan to host the interwiki off the .github.io won't work either
just neat to have, imo

scpwiki / interwiki

Add PR previews #10