Make wording a bit clearer

Author: RazerM

docs/source/tutorial.rst

@@ -25,7 +25,7 @@ which, like before, is the same as::
 
     x = await f(*args, **kwargs)
 
-An Outcome object may not be unwrapped twice. Attempting to do so will
-raise an :class:`AlreadyUsedError`.
+An Outcome object can only be unwrapped once. A second attempt would raise an
+:class:`AlreadyUsedError`.
 
 See the :ref:`api-reference` for the types involved.

src/outcome/_util.py

@@ -6,7 +6,7 @@
 
 
 class AlreadyUsedError(RuntimeError):
-    """An Outcome may not be unwrapped twice."""
+    """An Outcome can only be unwrapped once."""
     pass