[documentation] Add scaling tests

[jan-janssen]

How does pympipool compare to ThreadPoolExecutor and ProcessPoolExecutor ? It would be great to design benchmark studies. In addition, pympipool can be combined with the ProcessPoolExecutor when specifying the number of threads and running one pympipool process per node.

[jan-janssen]

This topic was initially brought up by @ligerzero-ai in https://github.com/orgs/pyiron/discussions/211#discussioncomment-8034046

[jan-janssen]

The benchmark was added in #264