Incorporate spec document into documentation

We have a [spec](https://github.com/dtr-org/unit-e-docs/blob/master/specs/spec_v1.0.md) in the unit-e-docs repository which contains a description of how block proposal and finalization work. We should incorporate this into the documentation in the docs.unit-e.io repository. The document also contains a glossary. This should be incorporated into the glossary of the docs repository (#8).
