Xamarin.Forms-Samples/HelloXamarinFormsCSharp/HolaXamarinFormsCSharp/packages/repositories.config

<?xml version="1.0" encoding="utf-8"?>
<repositories>
  <repository path="..\HolaXamarinFormsCSharp\HolaXamarinFormsCSharp.Android\packages.config" />
  <repository path="..\HolaXamarinFormsCSharp\HolaXamarinFormsCSharp.iOS\packages.config" />
  <repository path="..\HolaXamarinFormsCSharp\HolaXamarinFormsCSharp.WinPhone\packages.config" />
</repositories>