Updated console instructions for launching notes

When running the notes-server plugin, the node console had a message
that said to look in the JS console for a link to the notes page.  The
JS console log message no longer appears, so I have updated the node
console message to reflect how the notes page should be opened (pressing
the 's' key) as described in the documentation.

From the documentation and from https://github.com/hakimel/reveal.js/issues/381, it appears that pressing 's' is the proper way to launch notes now.