Address comments

doc/python/sphinx/grpc_asyncio.rst

@@ -24,12 +24,8 @@ gRPC Async API objects may only be used on the thread on which they were
 created. AsyncIO doesn't provide thread safety for most of its APIs.
 
 
-Enable AsyncIO in gRPC
-----------------------
-
-Enable AsyncIO in gRPC Python is automatic when instantiating gRPC AsyncIO
-objects (e.g., channels and servers). No additional function invocation is
-required.
+Blocking Code in AsyncIO
+------------------------
 
 Making blocking function calls in coroutines or in the thread running event
 loop will block the event loop, potentially starving all RPCs in the process.

src/python/grpcio/grpc/_cython/_cygrpc/aio/common.pyx.pxi

@@ -169,7 +169,7 @@ async def generator_to_async_generator(object gen, object loop, object thread_po
     await future
 
 
-if PY_MAJOR_VERSION >=3 and PY_MINOR_VERSION >=7:
+if PY_MAJOR_VERSION >= 3 and PY_MINOR_VERSION >= 7:
     def get_working_loop():
         """Returns a running event loop."""
         return asyncio.get_running_loop()
@@ -185,4 +185,5 @@ else:
         if loop.is_running():
             return loop
         else:
-            raise RuntimeError('no running event loop')
+            raise RuntimeError('No running event loop detected. This function '
+                             + 'must be called from inside of a running event loop.')