synchronize docstring: use recommended replacement for loop.run_trio

Author: shamrin

trio_asyncio/_base.py

@@ -413,7 +413,7 @@ async def synchronize(self):
 
         This is a Trio-flavored async function.
 
-        From asyncio, call ``await loop.run_trio(loop.synchronize)``
+        From asyncio, call ``await trio_as_aio(loop.synchronize)()``
         instead of ``await asyncio.sleep(0)`` if you need to process all
         queued callbacks.