Clarify some points the Wednesday session got stuck on

By request at the end of mentor session, this:
- Adds a couple lines explaining suPHP
- Explains where the vhost file you need to edit is the first time it comes up
- Points out where in the WP install to stop and set up the DB (kind of weird that's not in the WP instructions)
- Fixes a couple minor inconsistencies (e.g. a reference to the old index page after changing it)
  - I'm not sure which way "turn on error logging" vs. "view errors in the browser" was supposed to go; I went with the second one because it's closer to what was already there.