This is a start of moving the VTK-m User's Guide into the VTK-m source.
This is only the start of the process. There are several goals of this
work.
1. Integrate the documentation into the source code better to better
keep the code up to date.
2. Move the documentation over to Sphinx so that it can be posted online
and be more easily linked.
3. Incoporate Doxygen into the guide to keep the documentation
consistent.
4. Build the user guide examples as part of the VTK-m CI to catch
compatibility changes quickly.
