title: git push origin master does not work
body: <p>Although, I could commit my change locally, I can not push to origin master</p>
  
  <p>I run</p>
  
  <pre><code>$ git remote add origin git@github.com:username/test.git
  </code></pre>
  
  <p>I get</p>
  
  <pre><code>fatal: remote origin already exists.
  </code></pre>
  
  <p>I run</p>
  
  <pre><code>$ git push -u origin master
  </code></pre>
  
  <p>I get</p>
  
  <pre><code>ERROR: Repository not found.
  fatal: The remote end hung up unexpectedly
  </code></pre>
  
  <p>What's wrong with this?</p>