Fix benchmark script and update the readme page with latest results

[masci]

Describe the bug In the past we were running benchmarks quite regularly for haystack and published results here. As the benchmarking script was not working anymore at some point, we stopped doing it and never found time to fix it. ​

[julian-risch]

@Timoeller brought up that we should include QA training and evaluation in the benchmarks as well to make sure that we do not break this core functionality with new releases.