Add to maintainer offboarding procedures for special cases

[d33bs]

I like the language additions here. I wonder if we should include a maintainer offboarding process as well.

I imagine this would be a voluntary decision, but are there any other scenarios that we should delineate for offboarding?

Creating this issue to explore how to add to the existing offboarding procedures.

Originally posted by @gwaybio in #487 (review)

[d33bs]

We could get more thorough here and think through if we want to remove maintainers based on inactivity, but I don't know how to make that process fair and useful at this time. PEP 13 highlights an ejection process that might be helpful; maybe we could adopt something like this to be on the safe side (two-thirds vote to eject from other existing maintainers means involuntary offboarding of maintainer status within Pycytominer). We could peel this off into another issue for further discussion. Thoughts?