Add todo for custom weight type for Dijkstra's algorithm

src/algorithms.rs

@@ -27,6 +27,7 @@ pub struct DijkstraResult<V: Copy> {
     pub predecessors: VertexMap<V, Option<V>>,
 }
 
+// TODO: Generalize the return type of the weight function.
 pub fn dijkstra<G, W>(graph: &G, source: G::Vertex, weight: W) -> DijkstraResult<G::Vertex>
 where
     G: GraphTopology,