Update documentation to better reflect the current state of the driver

[heuristicus]

The documentation has been out of date for some time. This revises the documentation and brings it more or less up to date with the current state of the driver.

There are some things missing which I can't write documentation for:

• [ ] Arm stuff (Perhaps @maubrunn or @mfheinemann could fill in some detail)
• [ ] EAP/velodyne stuff (Maybe @jeremysee2 has insight)

I have added a file for describing how arm interaction works, but just put a list of services associated with the arm.

[heuristicus]

Merged. More complete updates to the documentation should be added separately later by people who have access to those components or wrote the current driver implementation.