In Superluminal, go to File > Load Ship. The window that appears is the ship browser. At the top of it, there are two fields, and two "Browse" buttons. You have to set up both fields correctly for the ship lists to load.
The upper field is for
data directory - this is the folder containing all of the txt and xml files. Click on the button by the upper field and browse to that directory, click on it and select "OK".
Next, the lower field - it is for
resources directory - this is the folder that stores all the images from the game. It should contain three directories: "audio", "fonts" and "img". Press the lower "Browse" button and navigate to that directory, click on it, and select "OK".
If you've done everything correctly, the ship lists will appear and you'll be able to select a ship to load. You won't have to repeat that process again, unless you move the directories somewhere.
Should you screw up though, and link a wrong directory, the app
might start crashing on startup; in that case, delete superluminal.ini and try again.
If it'll be of any help,
that's how it's set up on my PC.
I'll try to write up a guide of sorts tomorrow, or some other time...