Document the Basis blockchain

Describing the models, permissions, and rationale would make it easier for people to understand how and why it's put together the way it is. Things to note:

• The object types (companies (syndicate/private/etc), members, products, orders, labor, resources, cost tags)
• Permissions and roles
• Algorithms (costing, aggregate tracking)
• Scalability/blockchain library implementation (Exonum)
• Compromises (bureaucrats vs democratically-selected values, free-form occupations, etc)
• Contributing guidelines