Updated versioning doc to explain why sub components needs updates

Why not just say:

When it's time to branch between maintenance (eg., 4.2.x) and master branch, you should upversion your  features & plugins:
* in the maintenance stream to *a.b.x+1* (eg., 4.2.1, 4.2.2), and 
* in the master stream to *a.b+1.0* (eg., 4.3.0) or, if you can guarantee your master branch stuff works w/ the previous version of Eclipse, then *a.b.10x* (eg., 4.2.100, 4.2.101)