Use a materials science example on the overview

[kysrpex]

Currently, two examples are used:

• A city, for the linked data and simulation data transfer (to database) example.
• Fluid and molecular dynamics coupling.

Ideally, only one example should be used for the whole section, and this example should belong to the realm of materials science. Since SimPhoNy was born to support it, most users will come from this domain.