Refer a friend, contact, random person on the internet, or forums full of people, get 200 Triderium per!
So the codes aren't that long. Find it at your command center or triderium reactor. Click the gear icon in the lower left of the screen, aka settings to enter this code. You can only enter one referal code ever, but other promotional codes will go there later.
There are some bug fixes, and maybe some features I forgot to document. ;)
Enjoy.