Document maven coordinates of JARs in Moneta User Guide

[msgilligan]

I'm upgrading to the JPMS versions (from the BP versions) and am confused as to the difference between the org.javamoney and org.javamoney.moneta Group IDs on Maven Central.

(specifically I'm getting error: module not found: org.javamoney.moneta.convert when building with Gradle.)

The User Guide doesn't tell me which Maven coordinates to use, or explain the difference between the difference convert-* JARs.

[msgilligan]

I figured out my issue (need to consistently use the org.javamoney.moneta Group ID and artifacts) , but I still think the User Guide should document this.

[keilw]

@msgilligan Would you have a PR for that in the Asciidoc?