Mention exception chaining in contextmanager.__exit__

Author: johnslavik

Doc/library/stdtypes.rst

@@ -5357,8 +5357,8 @@ before the statement body is executed and exited when the statement ends:
    to suppress the exception and continue execution with the statement immediately
    following the :keyword:`!with` statement. Otherwise the exception continues
    propagating after this method has finished executing. Exceptions that occur
-   during execution of this method will replace any exception that occurred in the
-   body of the :keyword:`!with` statement.
+   during execution of this method will be propagated on top of any exception that
+   occurred in the body of the :keyword:`!with` statement.
 
    The exception passed in should never be reraised explicitly - instead, this
    method should return a false value to indicate that the method completed