Updating dox for mod_rest. Ideas expressed / clarified: 1) Making clear that mod_rest isn't to be installed under VirtualHosts AND as a component. 2) Understanding some of the implications of this choice: A) Changes to user authentication B) How it affects subdomains 3) More consistent use of domain names for clarity. 4) Using different heading sizes to show scope of section. Essentially, I added all the tidbits I had to clarify in getting this to work in my own example.

# Introduction

This module sends a [version query][xep0092] to clients when they
connect, and logs the response, allowing statistics of client usage to
be recorded.

Note that since this is per connection, there will be a bias towards
mobile clients on bad connections.

## Example

    info    Running Running Swift version 4.0