Update readme: Add link to demo

[t11r]

No description provided.

[ipf]

What do you think about adding a demo manifest to the link, instead of the plain viewer?

[t11r]

That’s a nice idea, any suggestions?

It might be even better to add a selection of manifests to the demo, like Mirador does, but this would take some time.

[ipf]

I'd take either one from the SUB or one with a lot of IIIF-features to show off ;)

[t11r]

It would be quite hard to find a manifest that is visually pleasing and includes all supported features (but none of the unsupported ones 😉). Let’s delay this, compile a list of manifests and add it to the demo (and the website as well).