You also need to install the Python requirements on Linux.
Port 21024 is in the default StarryPy congfig. Ports above 21025 are specified in the default Starbound config, and might become used. 21024 seems like a suggestion less-likely to cause headaches down the road.
Merge pull request #91 from flamsmark/readme-improvements

Readme improvements
Merge branch 'master' into development