title: pip errors during odoo 10 installation on centos 6.8
body: <p>I'm new to odoo, trying to insatll odoo 10 community edition on CentOS 6.8. I'm following their <a href="https://www.odoo.com/documentation/10.0/setup/install.html" rel="nofollow noreferrer">documentation</a>. I'm stuck on </p>
  
  <pre><code>"pip install -r requirements.txt"
  </code></pre>
  
  <p>Getting the following error.</p>
  
  <pre><code> Error: pg_config executable not found.
  
      Please add the directory containing pg_config to the PATH
      or specify the full executable path with the option:
  
          python setup.py build_ext --pg-config /path/to/pg_config build ...
  
      or with the pg_config option in 'setup.cfg'.
  
      ----------------------------------------
  Command "python setup.py egg_info" failed with error code 1 in /tmp/pip-build-5jzK4x/psycopg2
  </code></pre>
  
  <p>P.S  I have already installed " python-devel postgresql-devel"</p>