[WIP] Add governance document

[kabilar]

• Based on the GPT-5 prompt below, and then manually curated:
  • Please create a governance document for the DANDI Archive project. This document should apply to all sites (https://dandiarchive.org/, https://about.dandiarchive.org/, https://hub.dandiarchive.org/), organizations (https://github.com/dandi/, https://github.com/dandisets, https://github.com/dandizarrs) and all their repositories. The source code for the DANDI Archive is available here: https://github.com/dandi/. Format this document in markdown. Here are some example governance documents from other projects: https://bids.neuroimaging.io/collaboration/governance.html?h=governance, https://github.com/nebari-dev/governance, https://github.com/cncf/project-template/blob/main/GOVERNANCE-subprojects.md. And discuss who will review and merge pull requests.
• I will add the remaining sections later this week
• Once approved, update the following in the document:
  • Effective Date
  • Status