title: How to `--assume-unchanged` file in project?
body: <p>I have config file: <code>conf/local.conf</code> I run next command for it:</p>
  
  <pre><code>git update-index --assume-unchanged local.conf
  </code></pre>
  
  <p>and it is OK until I switch to another branch or pull.</p>
  
  <p>How to preserve <code>--assume-unchanged</code> flag between branches?</p>
  
  <p><strong>UPD</strong><br>
  Some examples what is coming on:</p>
  
  <pre><code>$ git checkout 296-ToS-component 
  error: Your local changes to the following files would be overwritten by checkout:
      conf/local.conf
  Please commit your changes or stash them before you switch branches.
  Aborting
  $ git checkout -f 296-ToS-component 
  error: Entry 'conf/local.conf' not uptodate. Cannot merge.
  </code></pre>
  
  <p>I want it works as next:</p>
  
  <ol>
  <li>conf/local.conf is saved</li>
  <li>Branch is switched</li>
  <li>conf/local.conf is replaced by saved version</li>
  </ol>