title: pip requirements.txt with alternative index
body: <p>I want to put all the requirements of a repoze Zope2 install in a pip <a href="http://pip.readthedocs.org/en/1.1/requirements.html#the-requirements-file-format" rel="noreferrer">requirements file</a>. Most of the repoze packages don't seem to be on PyPi, but there's an alternative PyPi index for them <a href="http://dist.repoze.org/zope2/2.10/simple/" rel="noreferrer">here</a>. But I can't figure out how to tell pip to use that index together with a requirements file. For single packages, it's easy</p>
  
  <pre><code>pip install zopelib -i http://dist.repoze.org/zope2/2.10/simple/
  </code></pre>
  
  <p>I tried the following</p>
  
  <pre><code>pip install -r requirements.txt -i http://dist.repoze.org/zope2/2.10/simple/
  </code></pre>
  
  <p>or in my requirements.txt all kind or permutations of these:</p>
  
  <pre><code>zopelib -i http://dist.repoze.org/zope2/2.10/simple/
  zopelib --index http://dist.repoze.org/zope2/2.10/simple/
  -i http://dist.repoze.org/zope2/2.10/simple/ zopelib
  </code></pre>
  
  <p>or (because the <a href="https://pip.readthedocs.org/en/1.1/requirements.html#indexes-find-links" rel="noreferrer">documentation</a> says "Note that all these options must be on a line of their own.")</p>
  
  <pre><code>--index http://dist.repoze.org/zope2/2.10/simple/
  zopelib
  </code></pre>
  
  <p>So, what's the correct way of telling pip to use <a href="http://dist.repoze.org/zope2/2.10/simple/" rel="noreferrer">http://dist.repoze.org/zope2/2.10/simple/</a> as index?</p>