Revise documentation

[amritpurshotam]

The documentation for Baobab has been written over the past two years by many contributors and so lacks a single cohesive voice. This issue aims to resolve that by revising the documentation and in so doing lowers the barrier to entry for new contributors while also at the same time minimizing the onboarding costs.

The updates to the documentation will be inspired by the following

• Divio describes the different kinds of documentation
• Awesome Readme contains a list of good READMEs and further articles for what makes a good README

Some additional sections to include

• Pull request checklist (each point will link to some documentation) - Migrations and merges - Tests - Routes - Authorisation decorators - Merging in latest develop
• Database ERD (additionally focus on ERDs for the application model and review models separately)
• Explanation of the user roles/personas
• Code tours
• Screenshots of perhaps of the front end for each stage in the process