[Documentation] Users of executorlib

[jan-janssen]

I guess it is helpful to collect examples of how executorlib is used in other projects:

Executors

• Use executorlib directly pylammpsmpi#371 - pylammpsmpi is currently transitioning to use executorlib Executors
• https://github.com/pyiron/pyiron_base - is using executorlib Executors
• Wrap executorlib executors pyiron_workflow#678 - pyiron_workflow is using executorlib Executors

Prototypes using executors

• https://github.com/pyiron-dev/pipefunc-executorlib
• https://github.com/pyiron-dev/executorlib-emcee
• https://github.com/pyiron-dev/executorlib-omp4py

Custom Spawners

• CondaSpawner - derived from SubprocessSpawner class conda_subprocess#144 - conda_subprocess defines it is own executorlib Spawner