Record-keeping for subteams

[jezdez]

Since we're now starting to add a few non-project subteams such as the communications and infrastructure team, we should start tracking them for easier maintenance via PRs and record-keeping.

Maybe it would suffice to have a SUBTEAMS.md that lists the teams from top to bottom, including their team charter, members and important links like chat rooms etc.

If we're making sure the content is nicely formatted, we could even possibly render it as part of the conda-incubator/conda-dot-org work when it's ready?

[jaimergp]

Reopening for #313