add notes some magic don't work yet

docs/source/interactive/autoawait.rst

@@ -132,6 +132,15 b' allow ``IPython.embed()`` to be nested. Though this will prevent usage of the'
 You can set explicitly a coroutine runner for ``embed()`` if you desire to run
 asynchronous code, the exact behavior is though undefined.
 
+Effects on Magics
+=================
+
+A couple of magics (``%%timeit``, ``%timeit``, ``%%time``, ``%%prun``) have not
+yet been updated to work with asynchronous code and will raise syntax errors
+when trying to use top-level ``await``. We welcome any contribution to help fix
+those, and extra cases we haven't caught yet. We hope for better support in Cor
+Python for top-level Async code.
+
 Internals
 =========
 

docs/source/whatsnew/pr/await-repl.rst

@@ -77,6 +77,12 b' The introduction of the ability to run async code had some effect on the'
 ``IPython.embed()`` API. By default embed will not allow you to run asynchronous
 code unless a event loop is specified.
 
+Effects on Magics
+-----------------
+
+Some magics will not work with Async, and will need updates. Contribution
+welcome.
+
 Expected Future changes
 -----------------------