[RFC] proposed user doc for nested trees

[Alexander Belchenko]

I have one question very important to me:

Does nested trees will support double (recursive) nesting?
I.e. when I want to create mega-project that in turn will consist 
several subprojects aka nested trees?

Use case for this scenario: we're build resulting installer for our 
product from several loosely coupled components. Many of these 
components are actually nested trees (currently we're using scmproj 
plugin to manage it).