Create project criteria/guide for OCI proposals

[estesp]

A start was made on thinking about how various repos within the OCI currently fit into a set of project types (specs, reference implementations, helper libraries). We need to finish this effort and publish it to provide guidance to both the TOB (for voting on new proposals) as well as future potential submissions to make is less vague on what fits in the OCI scope.

A start on this effort is located in the TOB call notes: https://hackmd.io/kKl1ECKnSLWhgk7dZ2WUFQ#Categorizing-Project-Types

[estesp]

cc: @opencontainers/tob

[estesp]

Attempting to start this work in #76

[vbatts]

Is this deprecated now by the Working Group language?