Document a workflow for investigating performance regressions.

[ian-r-rose]

cc @hayesgb, who expressed some interest in this

[ncclementi]

I think this PR makes sense to merge it once we are using package sync. Otherwise, there are a couple of things you need to tweak to be able to use it. Or we could temporarily document those tweaks, and then once the package sync PR is merged, remove them.

Thoughts?

[ian-r-rose]

I'll clarify some of the things you ran into. But I agree, this doesn't make much sense to merge until package_sync is in

[ncclementi]

@ian-r-rose should we fix conflicts and get this one in since package sync is already in?

[ian-r-rose]

Good point, I forgot about this one! Updating now...

[ian-r-rose]

Okay, should be ready

[ncclementi]

Thank you Ian! I'll wait for CI and then I'll merge it.

[ncclementi]

Failures and regressions are known flaky and noisy repspectively. SInce this is purely docs I'll go ahead and merge it in.
Thank you @ian-r-rose for your work here.