Add demo for CF Pages to @next

[saibotsivad]

I was also looking into using Worktop for Pages, so based on conversation in #145 I went ahead and made a demo in worktop@next so that information would be easy to find later.

[lukeed]

I thought about making this an example too, but it's a little tough because it doesn't make sense as an /examples entry on its own. The rest of that directory can be deployed on its own, but this PR (and the demos from issue) don't as they need a static site to go along with it for it to make sense... and to have some npm run build command put a _worker.js in the correct location, etc.

So instead I was thinking more along adding this as a documentation page on the (upcoming) site. WDYT?

[saibotsivad]

Hmm yeah, I think that could make sense. Maybe you could add the documentation label to the issue?

Basically, I just don't want this information to get lost in between now and the eventual website / worktop@next release. 😅