Documentation how ISAAC works

[psychocoderHPC]

@kimjohn1 asked https://github.com/ComputationalRadiationPhysics/picongpu/issues/3622#issuecomment-848813681 about some documentation on how ISAAC internally works.

Let us collect paper we can put later into the ISAAC documentation in this issue.

CC-ing: @FelixTUD

[psychocoderHPC]

• Diploma thesis (German): In-Situ Visualisierung und Streaming von Plasmasimulationsdaten
  • https://zenodo.org/record/55329/
• In situ, steerable, hardware-independent and data-structure agnostic visualization with ISAAC
  • http://dx.doi.org/10.14529/jsfi160403

[FelixTUD]

• ISAAC extension on particle rendering (only German)
  • https://zenodo.org/record/1423296
• ISAAC Documentation (outdated right now but still helpful)
  • https://computationalradiationphysics.github.io/isaac/