Update contributor guide

[tomtitherington]

Summary

Create the 'Contributor Guide' section of the documentation.

Details

• Deliverables: What should be delivered? Go into detail where necessary, this is usually best written as a list of tasks.

Local setup guide

• [ ] Creating the Postgres database
• [ ] Seeding database
• [ ] Setting up the environment variables
• [ ] Installing dependencies
• [ ] Running the project

Docker setup

• [ ] Creating the Postgres database
• [ ] Seeding database
• [ ] Setting up the environment variables
• [ ] Installing dependencies
• [ ] Running the project

IDE setup

• [ ] Git pre-hooks
• [ ] C spell

Frontend development

• [ ] Folder structure
• [ ] ESLint
• [ ] Prettier (prettierrc.js)
• [ ] Best practices
• [ ] Style guide

Backend development

• [ ] Overview of the tech stack (different services .. etc)
• [ ] Mypy
• [ ] Flake8
• [ ] isort
• [ ] Folder structure
• [ ] Open API generator / Development workflow
• [ ] Best practices ( something about the open-api generator here)

Dependent Tasks

• [ ] #26

[tomtitherington]

Twenty do this well