Improve README file

[mario-nt]

The README file is lacking an important step for getting the GUI up and running, the user has to create a .env file and copy the content of the .env.local (included in the repo), because if not present, the calls to the API will not work and will return an undefined error.

That step is included in the /bin/install.sh file, but it should be included in the README file as it can lead to a lot of frustration to an end user as the GUI will not work.

The .env file changes the API URL from http://localhost:3001 to http://localhost:3001/v1.

The error: