title: Git warning: push.default is unset; its implicit value is changing
body: <p>When I push to remote in Git, I get this warning:</p>
  
  <pre><code>warning: push.default is unset; its implicit value is changing in
  Git 2.0 from 'matching' to 'simple'. To squelch this message
  and maintain the current behavior after the default changes, use:
  
    git config --global push.default matching
  
  To squelch this message and adopt the new behavior now, use:
  
    git config --global push.default simple
  
  See 'git help config' and search for 'push.default' for further information.
  (the 'simple' mode was introduced in Git 1.7.11. Use the similar mode
  'current' instead of 'simple' if you sometimes use older versions of Git)
  
  To **********************************
     6b9a6d2..3ab1eab  master -&gt; master
  </code></pre>
  
  <p>What does this warning mean and what should be done about it?</p>