You need a variable to store the total of the non-six rolls and a loop so that it repeats until a 6 is rolled.
I don't know python, so this is somewhat pseudocode - based on the code above...
total = 0
roll = 0
while ( roll != 6 ):
roll = random.randint(1, 6)
total = total + roll
print("You rolled a ", roll, " Your total score is: ", total)
print("You rolled a 6, game over")
Edit: My indentation is wrong ( I think Python cares about that stuff ) so copy / pasting my code probably won't work !