Add documentation on how to run the Burr UI server

**Is your feature request related to a problem? Please describe.**
There is no section in the documentation on how to run the Burr UI server.

**Describe the solution you'd like**
1. create a section in the documentation about the UI.
2. provide details on installation
3. how to run it
4. document optional commands, e.g. creating demo data or not
5. document what one can do with the UI: see things by project, run some demos, etc.

**Describe alternatives you've considered**
N/A

**Additional context**
This should be the reference documentation to point someone to how to install / run things.