i believe the text book way is like anything that has a fill plug......fill it till it starts to run out......or, fill it untill you can atleast touch the oil level with your pinky finger if you can get it into the fill hole....
The "text book" says to fill with 2 quarts of synthetic fluid... However, you typically can put in about 2.5 quarts until it starts weeping out of the filler hole. Most people just fill until it drips out the filler hole..
Make sure you are putting in friction modifier with the new fluid. Otherwise your limited slip is gonna bind on you going around turns...
Just did mine last week with Mobil 1 and friction modifier. It took about 2.7 bottles (liters). As said above, you will know when it is full. It will come out the fill plug.