Clarified error message for missing profile

pycapo/models.py

@@ -46,7 +46,7 @@ class CapoConfig:
         elif 'CAPO_PROFILE' in os.environ:
             self.profile = os.environ['CAPO_PROFILE']
         else:
-            raise ValueError('could not determine profile')
+            raise ValueError('Expected profile via CAPO_PROFILE or \"profile\" kwarg, found neither')
 
         if 'path' in kwargs and kwargs['path']:
             self._path = kwargs['path']