title: adding tooltip for nodes in python networkx graph
body: <p>I created a directed graph using <code>networkx.DiGraph</code> then plotted it using <code>networkx.draw_spring(graph)</code>, so all the nodes of the graph have some details stored in a list of dictionaries.</p>
  
  <p>How to add something like a "tooltip" to view these details on mouse hover on each node? If this is possible, how to make this "tooltip" always visible for all nodes, not just by hovering?</p>