[profile] added example for ProfilerContext (#349)

colossalai/utils/profiler/prof_utils.py

@@ -35,15 +35,25 @@ class ProfilerContext(object):
     """
     Profiler context manager
     Usage:
-    from colossalai.utils.profiler import CommProf, ProfilerContext
-    from torch.utils.tensorboard import SummaryWriter
-    cc_prof = CommProf()
-    with ProfilerContext([cc_prof]) as prof:
-        train()
-    writer = SummaryWriter('tb/path')
-    prof.to_tensorboard(writer)
-    prof.to_file('./prof_logs/')
-    prof.show()
+
+    ```python
+        world_size = 4
+        inputs = torch.randn(10, 10, dtype=torch.float32, device=get_current_device())
+        outputs = torch.empty(world_size, 10, 10, dtype=torch.float32, device=get_current_device())
+        outputs_list = list(torch.chunk(outputs, chunks=world_size, dim=0))
+
+        cc_prof = CommProfiler()
+
+        with ProfilerContext([cc_prof]) as prof:
+            op = dist.all_reduce(inputs, async_op=True)
+            dist.all_gather(outputs_list, inputs)
+            op.wait()
+            dist.reduce_scatter(inputs, outputs_list)
+            dist.broadcast(inputs, 0)
+            dist.reduce(inputs, 0)
+
+        prof.show()
+    ```
     """
 
     def __init__(self, profilers: List[BaseProfiler] = None, enable: bool = True):