feat: Add benchmarking section to engine documentation with benchmark image

Author: miskibin

docs/source/_static/engine_benchmark.png

@@ -82,4 +82,12 @@ the ``get_best_move`` method::
             move = random.choice(list(board.legal_moves))
             if with_evaluation:
                 return move, 0.0
-            return move
+            return move
+
+
+Benchmarking the Engine
+-----------------------
+
+.. image:: _static/engine_benchmark.png
+   :alt: Engine Benchmark Results
+   :width: 600px