[vtkusers] VTK build instructions cleanup

[David Doria]

> ...with_out_ CMake... Right?

Yes, sorry for the typo - WITHOUT CMake.

> Indeed, especially since there are lot of tutorials on this topic out here
> giving - to my option - false advice, like copying header files or libraries
> to the project etc.

Yea, even though it is not recommended, there are surely "bad" and
"worse" ways to do it :)

David