Fix typo

Co-authored-by: Michael Abbott <[email protected]>

Author: coretl

docs/explanations/asyncio-cothread-differences.rst

@@ -67,7 +67,7 @@ While the same example written using asyncio is::
     builder.aOut('AO', on_update=update_ao)
 
 Note that because ``something_that_yields_control()`` is an ``async def``,
-``update_ao()`` needs to be to.
+``update_ao()`` needs to be too.
 
 .. seealso::
 
@@ -96,4 +96,3 @@ keep to one if possible.
 .. _aio-libs: https://github.com/aio-libs
 
 
-