title: Reading app.config from .NET Standard 2.0 library
body: <p>I'm creating a .NET Standard 2.0 library to be consumed from a .NET Framework 4.6.1 application.<br>
  This library needs EF Core, but I can't figure out how to read the app.config.</p>
  
  <p>In a .NET Framework library I would initialize my DBContext like this:</p>
  
  <pre><code>protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
  {
      optionsBuilder.UseSqlServer(ConfigurationManager.ConnectionStrings["MyDatabase"].ConnectionString);
  }
  </code></pre>
  
  <p>But I can't do it since ConfigurationManager is nowhere to be found in .NET Standard 2.0.<br>
  How can I read the configuration file from a .NET Standard 2.0 library?</p>