title: React Navigation: Access pages not in TabNavigator
body: <p>I have 3 main screen components which are the tabs in my <code>TabNavigator</code>: Feed, Discover, and Me. I also have other pages which I need to be able to navigate to from those 3 main pages. However, I can't just nest a <code>StackNavigator</code> in my <code>TabNavigator</code> because some of my subpages, I need to be able to access from every tab.</p>
  
  <p>This is a lot like how apps like Instagram work. Say for example you're looking at your feed and you tap on someone's username and their page comes up. However, this user's page is also accessible from your user page by finding their username in a list of your followers.</p>
  
  <p>How should I configure my navigation?</p>