message: add documentation for remove_node
diff: @@ -184,6 +184,8 @@ where
  }
  /// Return `true` if node `n` was removed.
  + ///
  + /// Computes in **O(V)** time, due to the removal of edges with other nodes.
  pub fn remove_node(&mut self, n: N) -> bool {
  let links = match self.nodes.swap_remove(&n) {
  None => return false,
  