title: Interactively merge files tracked with git and untracked local files
body: <p>I use a couple of software packages (like gitlab) that you install by cloning from their git repo. They typically come with some <code>config.example</code> (under version control), which you copy to your own <code>config</code> file (not under version control or even ignored in <code>.gitignore</code>) and adapt to your needs.</p>
  
  <p>When the upstream package is updated and for example changes the config file options that will obviously only be reflected in <code>config.example</code>.</p>
  
  <p>Is there a chain of git commands that i'm missing that can help me compare the changes of <code>config.example</code> to the new one in <code>upstream/HEAD</code> and maybe even merge them interactively into my local <code>config</code> file?</p>
  
  <p>Would be awesome if i could get something like the interactive patch mode in <code>git add/commit --interactive</code>.</p>