[vtkusers] pipeline documentation/intro

[Galen Wilkerson]

Anyone know the best way to tell which classes belong to which parts of 
the pipeline?  I'm new to this, but it seems like the general info online 
is:  "hey, there's this pipeline thing, you have to learn about it!!", 
then a black hole of information.  Same goes for the graphical model, 
which is evidently the other thing to understand.

-Galen