clarify this is a simplified example

Change-Id: I3a9a4f8562d57091031386785354c32ec316cd88

Author: zzzeek

docs/build/synopsis.rst

@@ -177,7 +177,9 @@ other greenlets anywhere within the execution of that greenlet::
 
 Above, the ``send_receive_logic()`` function is called within a greenlet that
 itself links to a parent greenlet that's local to the :func:`.async_def`
-callable (this is the normal way that greenlet works)::
+function (this is the normal way that greenlet works).  Below we illustrate
+a **simplified** version of :func:`.async_def` that does not include details
+like exception handling and other robustness regarding arguments::
 
     async def async_def(
         fn: Callable[..., _T],
@@ -273,5 +275,7 @@ True, then we know the function completed; we return the result!
     # no more awaits; so this is the result!
     return result
 
-
-Minus error handling and some other robustness details, that's the whole thing!
+The real function has a more elements within the loop to accommodate for
+exceptions thrown from the callable, as well as other features to check that
+awaitables ran if this was expected.   But minus those details, the single loop
+is pretty much the whole thing!