[Request] Add a contribution/development guide

[pvharmo]

Hi! I find this project is very interesting, and I would be interested in contributing. However, there are many commands in the package.json which is a bit confusing. I manage to set up a development environment that works, but there is no hot-reload, so I have to rebuild all the application between each change and none of the tests are working.

I am currently using npm run build:dev && npm run start:dev for development and npm run build:test && npm run test to run the tests.