make installation smoother for geeks+issues

there are still some significant obstacles to smooth wagn installation, even for competent geeks.  they include:

• unix-specific documentation -√? definitely some improvements here (no more sudo)
• √? warnings about new relics plugin
• √ separate gem installs
• make rake:copy_configs (and have that do all the file copying)
• expect no needed initial changes to wagn.rb. We should add lots of comments to sample_wagn.rb, and then just refer them there for customization / fine tuning.
• similarly, we should add a bunch of comments to sample_database.yml and just point them there on the installation page.