Criteria for an institution to be considered a supporter of Dask

This is related to #32, but smaller in scope.

We currently have a group of contributors who meet weekly to discuss maintenance of Dask. To be a part of this group, we ask that you have 8+ hours a week to spend working on general maintenance and "core" tasks - things that are generally useful, rather than your own specific use cases. This team is currently composed of a people from several different companies, with this "dask core work" being part of their job description (i.e. their employer is on board with this arrangement, and is effectively funding dask development).

A list of companies supporting dask is displayed at the bottom of our main page (https://dask.org/). This list includes some institutions that have funded Dask (currently, as well as previously), as well as a few (but *not* all) of the companies currently employing the core Dask team.

A question then arises - *how does an institution get added to this list, specifically with regards to funding a developer to help handle core maintenance tasks?*

I don't believe we've codified this in our governance anywhere. Colloquially, we require:

- At least 8 hours a week of time be spent working on issues and projects deemed "core" (decided during the weekly meetings)
- Participation in the weekly meetings

Assuming we like the above requirements, the missing components are:

- How long must the above be done for before we give "supported by" status?
- How long must the above be stopped for before we remove this status?

This is a tricky question. We want to reward good actors early, to encourage good behavior. But we don't want a bad actor to be able to game the system - funding a dev for just long enough to get status and then stop. We also want a smooth process for removing institutions if the requirements are broken, while also acknowledging that gaps in support will likely occur because people take vacations/have off weeks.