title: Can pip install from setup.cfg, as if installing from a requirements file?
body: <p>According to the <a href="https://setuptools.readthedocs.io/en/latest/setuptools.html#configuring-setup-using-setup-cfg-files" rel="noreferrer"><code>setuptools</code> documentation</a>, <code>setuptools</code> version 30.3.0 (December 8, 2016) "allows using configuration files (usually <em>setup.cfg</em>) to define package’s metadata and other options which are normally supplied to <code>setup()</code> function". Similar to running <code>pip install -r requirements.txt</code> to install Python packages from a requirements file, is there a way to ask <code>pip</code> to install the packages listed in the <code>install_requires</code> option of a <code>setup.cfg</code> configuration file?</p>