Fix doc for loop.shutdown_default_executor()

After applying the suggestion from @1st1, this adjusts the surrounding wording and flow of the paragraph.

Author: aeros

Doc/library/asyncio-eventloop.rst

@@ -169,10 +169,10 @@ Running and stopping the loop
 
 .. coroutinemethod:: loop.shutdown_default_executor()
 
-   Schedule the closure of the default executor and wait for it to join all threads
-   :class:`ThreadPoolExecutor` to finish joining all of the threads. After
-   calling this method, a :exc:`RuntimeError` will be raised if
-   :meth:`loop.run_in_executor` is called while using the default executor.
+   Schedule the closure of the default executor and wait for it to join all of
+   the threads in the :class:`ThreadPoolExecutor`. After calling this method, a
+   :exc:`RuntimeError` will be raised if :meth:`loop.run_in_executor` is called
+   while using the default executor.
 
    Note that there is no need to call this function when
    :func:`asyncio.run` is used.