Fix broken example link in readme.md

[ethagnawl]

Fix broken link to example in README

[peteygao]

Technically the text should also be changed, since it's no longer an Emoji Chat Room demo, rather the example is an embedded Elm clock.

[ethagnawl]

Good point, @peteygao.

This is orthogonal to this PR, but while we're at it, I also had to do a bit of work to get the latest example working on my machine (updating react/dom, removing emojione-picker and using the published version of the library -- as opposed to the relative path). If the maintainers would be interested, I'd be happy to submit an additional PR containing those changes.

[peteygao]

@ethagnawl 👍

Really hoping all these improvement PR's are going to get merged by the repo maintainer(s) at some point. I'm having to do this manually in a forked repo to include all the fixes to present to my colleagues (we're using React, and I'd love to slowly introduce Elm).