Add how to start documentation

[frycz]

Motivation

I spent some time trying to run the application locally. I would like to share my findings in the form of a documented process and utility scripts. Hopefully, it will help other developers.

Here are a couple of issues which are solved in the PR:

• missing /socket.io/socket.io.js file
• client socket not listening on the local server
• running node server.js does not start the whole application, just the server. The database and the client need to be run separately.

What is improved/added

• information on how to point the client to the local server
• a command for running the database, the server and the client
• a node command for the map formatting
• node and bash commands for faster Docker image management

Alternative solution

I am open for discussion. Please share issues you face while running the application locally and how you deal with them.

How to test

• Clone the repository and checkout the branch. It is important to have a clean environment
• The link in README.md file should move the user to GETTING_STARTED.md document
• Following instructions in the GETTING_STARTED.md file should be clear and help the user to run the application
• All new commands in package.json work

Potential regressions

None

[Jerenaux]

Thank you for the time spent on doing this contribution, it's much appreciated!