title: ssh-keygen - how to set an rsa key with a certain username
body: <p>I just installed ubuntu and would like to set its rsa keys up with bitbucket/github. When I ssh-keygen the keys are generated as they should be</p>
  
  <pre><code>ssh-rsa AA...yBEz3pLL georgemauer@ubuntu
  </code></pre>
  
  <p>which is perfectly usable except the username part. In every rsa key I've generated previously, the username section read my email address:</p>
  
  <pre><code>ssh-rsa AA...yBEz3pLL gmylastname@gmail.com
  </code></pre>
  
  <p>No, it's not a major impediment but if I don't get this right it will drive me crazy. How, do I generate with rsa keys with an email username of my choice?</p>