message: inline doc example for node_indices
diff: @@ -938,7 +938,18 @@ impl<N, E, Ty, Ix> Graph<N, E, Ty, Ix>
  Externals{iter: self.nodes.iter().enumerate(), dir: dir, ty: PhantomData}
  }
  - /// Return an iterator over the node indices of the graph
  + /// Return an iterator over the node indices of the graph.
  + ///
  + /// For example, in a rare case where a graph algorithm were not applicable,
  + /// the following code will iterate through all nodes to find a
  + /// specific index:
  + ///
  + /// ```
  + /// # use petgraph::Graph;
  + /// # let mut g = Graph::<&str, i32>::new();
  + /// # g.add_node("book");
  + /// let index = g.node_indices().find(|i| g[*i] == "book").unwrap();
  + /// ```
  pub fn node_indices(&self) -> NodeIndices<Ix> {
  NodeIndices { r: 0..self.node_count(), ty: PhantomData }
  }
  