feat: allow specifying number of games via arg

[AndrewADev]

Leverage click (already a dependency) to accept a command line argument for specifying the number of games to play.

$ python ./rps-sim.py --games 15
Result: Player 1 draws
Result: Player 1 draws
Result: Player 1 loses
Result: Player 1 loses
Result: Player 1 wins
Result: Player 1 loses
Result: Player 1 draws
Result: Player 1 loses
Result: Player 1 draws
Result: Player 1 draws
Result: Player 1 draws
Result: Player 1 loses
Result: Player 1 loses
Result: Player 1 wins
Result: Player 1 draws
Simulation finished.