Update README

Reword description to draw attention to SNIPRoxy being a layer 4 proxy.
Remove upgrading node now that versions are updated from git describe.
Add -V to usage.
Add gettext-devel to RPM requirements.
Update RPM build disclaimer.
Update package descriptions

Updating descriptions to match README and man page, calling attention to
the fact that SNIProxy is a layer 4 proxy not an application level
proxy.