actual different nodes are a helpful example case

The original tutorial text is confusing for the primary reason that it doesn't actually talk about two separate nodes, but about two databases and two londiste workers running on the same machine.  This does cover a lot of ground, but if one actually expects to replicate across multiple hosts, it's unclear where changes need to be made.

This revised text thusly has two major improvements:

  (a) point to IP address, which is actually necessary esp for create-root, but in general.
  (b) de-conflate the name of the database and worker, one of which would be the same on all nodes in the real world, and one of which must always be unique.

It would be possible to change this so that it points at 127.0.0.1, but that's still likely to leave some ambiguity, and I think it is easier for one who wants to test this on a single machine to translate from an example with actual addresses.