Document how parent-child POM relationships, <modules/>, and <parent><relativePath/> works

Create a document that will describe how POMs can be related to one another in a multimodule build. Specifically, document:

• The parent-child relationship - how is this manifest in the POMs
• How does the <modules/> section work
• How does the <relativePath/> element of the <parent/> section work...and what is required in the <parent/> section?
• How to install ONLY the parent POM for a multimodule setup (mvn -N pom.xml at the top level)
• How to build an entire multimodule setup from one command (tie all of this together into a working example)

Related to this, but in another document, should be a list of things that are inherited (could be a link to somewhere else, if this documentation exists in other places). Also, the algorithm used to merge inherited and local POM sections should be in this other document.