Add introduction

[LudwigFriedmann]

Is your feature request related to a problem? Please describe. The introduction of the geometry chapter is still empty. We should introductionary sentences here.

Describe the solution you'd like In the introduction chaper, we should loose some words about

• What is a 3D asset/geometry?
• For which use cases are assets needed? (..., in our case: sensor simulation)
• What is the role of 3D exchange formats in OpenMATERIAL? (baseline that enables usage of existing processes)
• How do the OpenMATERIAL specifications build on/extend existing file formats and their specifications? (OM adds on the bare exchange formats and extends them for our use cases, e.g. semantic information, structure, coordinate frames, harmonized integration/usage in simulation, physics-based materials)
• What is the difference between reference 3D geometry and materials? (for the above mentioned use-cases, not only rendering materials, but physics-based sensor materials are needed)
• Is the standardization of 3D models specified by OpenMATERIAL separated from the standardization of materials in OpenMATERIAL? (tbd)
• How are materials referenced (brief introduction and reference to dedicated chapter here) (concrete description and chapter tbd)

Describe alternatives you've considered

Additional context

[LudwigFriedmann]

• How is this standard interacting with other ASAM standards, such as OpenSCENARIO, OpenDRIVE, OSI,... (brief introduction plus a reference to a dedicated chapter