title: Joining two networkx graphs on a single edge
body: <p>I need a graph with N clusters, that somewhat represents the structure of social networks. I planned to go about this by creating N graphs with barabasi albert structure, and then connecting them by a single node.</p>
  
  <pre><code>import networkx as nx
  
  a = nx.barabasi_albert_graph(10,2)
  b = nx.barabasi_albert_graph(10,2)
  
  nx.draw(a)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/oSUiu.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/oSUiu.png" alt="enter image description here"></a></p>
  
  <pre><code>nx.draw(b)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/OXyQc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OXyQc.png" alt="enter image description here"></a></p>
  
  <p>what I want is them connected like this:<a href="https://i.stack.imgur.com/lk2WF.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lk2WF.png" alt="enter image description here"></a>
  But I cannot see or find any simple way of doing this, are there any networkX functionality that can do just this?</p>