Cleanup of documentation and raise correct exception type

b_asic/architecture.py

@@ -402,8 +402,8 @@ class ProcessingElement(Resource):
         heuristic : str, default: 'left_edge'
             The assignment algorithm.
 
-                * 'left_edge': Left-edge algorithm.
-                * 'graph_color': Graph-coloring based on exclusion graph.
+            * 'left_edge': Left-edge algorithm.
+            * 'graph_color': Graph-coloring based on exclusion graph.
         """
         self._assignment = list(
             self._collection.split_on_execution_time(heuristic=heuristic)