specify the framework for matmul example. (#37)

Co-authored-by: Guoshuai Zhao <guzhao@microsoft.com>

examples/benchmarks/matmul.py

@@ -3,17 +3,16 @@
 
 """Model benchmark example for matmul with pytorch.
 
-Command to run:
+Commands to run:
   python3 examples/benchmarks/matmul.py
 """
 
-from superbench.benchmarks import BenchmarkRegistry
+from superbench.benchmarks import Framework, BenchmarkRegistry
 from superbench.common.utils import logger
 
 if __name__ == '__main__':
     context = BenchmarkRegistry.create_benchmark_context(
-        'matmul',
-        parameters='--num_steps=20',
+        'matmul', parameters='--num_steps=20', framework=Framework.PYTORCH
     )
 
     benchmark = BenchmarkRegistry.launch_benchmark(context)