Add a doc page about user expectations

[yck011522]

Add a page describing what users need to know in order to perform different tasks using compas_fab. This can go on the first introduction page or a deliciated page of its own.

Level 0 (Complete Layman / No Code)
Visualization

Level 1 (Typical users)
Define Robot Cell (Robot, Collision Environment, Tools, Workpieces)
Plan Motion
Plan Process

Level 2 (Advanced User)
Modify Robot Kinematics and Semantics (e.g. Planning Groups)
Custom Robot (e.g. multiple robots in cell)

Level 3 (Research level)
Extension with custom Motions and Planning Algorithms
Extension with custom Planning Backends
Configure planning parameters for individual planning backends

[jf---]

+1

A nice way to approach this is perhaps through the use of the admonitions module?

[yck011522]

@jf---
This is new to me. Does this require extra work to setup the doc building process?

Maybe I will draft the content first.