That's either going to be easy, or much trickier. If you want to tie it to an existing research, the just add the research in as a prerequisite to your entity.
Should look like that when you're finished.
If you want to make a new research, then you're going to have to copy one of the existing ship unlock ones with a new name, add it to the PlayerRace.entity file, then add that in as the needed research. You don't need to add .entity to the end in there, only the name.