GOVERNANCE: review and refine governance documents

[estesp]

Per discussion with the @opencontainers/tob members in March/April 2020, there are aspects to the OCI governance which are significantly out of date or simply related to the early construct under which the OCI was formed in 2016.

After the move of opencontainers.org to GitHub (see the work underway in https://github.com/opencontainers/opencontainers.org) we should be able to do this with a standard GitHub pull request/approve/merge workflow.

Part of this work needs to specifically deal with the question of TDC vs. TOB vs. maintainers of OCI projects:

• related: Update OCI charter to deal with project structure issue #2
• related: OCI TOB discussion: https://hackmd.io/kKl1ECKnSLWhgk7dZ2WUFQ#Notes (see item 2 TODO)