USER STORY: create Entity Relationship Diagrams

[alanjameschapman]

As a developer I can create ERDs so that I can define and visualise how database tables relate to each other.

Acceptance Criteria

• [x] Tables show relationship types e.g. 1-2-1
• [x] Tables show field types (fed into Models).

Tasks

• [x] Create diagrams in Lucidchart.

[alanjameschapman]

See ERD in README.