Add spotlight nest

Closes #338 (closed)

The NEST simulator (Helmholtz research field: Information) is a spiking neural network simulator for neuroscience research.

• Review link

Checklist for authors

• Add a link pointing to the review app

Checklist for reviewers

• Reference the corresponding issue in MR
• File size of images is not too large
• Update date_added attribute
• Centres are referenced by official names
• License is named by SPDX identifier if possible
• All links are pointing to the right place

/cc @frust45 @konrad @jandt-desy @christian.meessen