Both systems and map info are easy to input. The issue is the data, specially the system coordinates: I have absolutely no idea from where mojo is taking the information about system placement. The additional z coordinate of the system also can't be found on mojo's map.
The systems spatial coordinates are registered on the file map.js. The system information (resources, history, faction, crime status,...) are stored inside the systems.js file. Both of them are on the js/data/ folder.
Examples:
the Sol entry inside js/data/map.js (spatial coordinates)
"Sol": { "scale": 1, "coords": [ 0, 45, 0 ] },
The Nul system info on the js/data/systems.js general info)
"Nul": {
source: "https://robertsspaceindustries.com/comm-link/transmission/12804-Unlock-Nul-System",
ownership: "None",
planets: 5,
planetary_rotation: [],
"import": [],
"export": [],
crime_status: "Low",
black_market: ["Slaves"],
uue_strategic_value: "Grey",
blob: [
"Nul is a Classical Cepheid star, a yellow supergiant that pulsates (swelling 10-15% in size and luminosity) approximately every few months. Due to the variable nature of the star, attempts to terraform have not been successful, so the system was simply abandoned. To the public (and most law enforcement) there is nothing of interest in the system. To a sliver of the criminal element, it's the site of a slave market, set up for randomly determined times and locations to keep it under the radar.",
"This guide can not, in good conscious, advise pilots to engage in human trafficking. Even with a less human set of morals, it would be ill-advised: modern slavers are just as likely to take a hapless cargo pilot right alongside his victims. The only advice is: avoid at all costs.",
]
}
The structure is always the same. I could easily make a pull request containing the additional system data (or a fork, if the original dev is no longer active), but like I said I have absolutely no idea from where folks are getting that data. The only data source I know is those System unlock pages and some Jump Point issues.