title: Add an implementation of 'IDesignTimeDbContextFactory<ServicesDbContext>' to the project error while creating a migration step in .NET core 2.0
body: <p>I had a .NET core 1.0 webapp working fine. I had to upgrade to .NET Core 2.0. I also had to add a migration step for my SQLite database. </p>
  
  <p>If I launch this command:</p>
  
  <blockquote>
    <p>Add-Migration MyMigrationStepName</p>
  </blockquote>
  
  <p>I get this error:</p>
  
  <blockquote>
    <p>Unable to create an object of type 'ServicesDbContext'. Add an
    implementation of 'IDesignTimeDbContextFactory' to
    the project, or see <a href="https://go.microsoft.com/fwlink/?linkid=851728" rel="noreferrer">https://go.microsoft.com/fwlink/?linkid=851728</a> for
    additional patterns supported at design time.</p>
  </blockquote>
  
  <p>I've seen plenty of answers on SO and on other blogs and website but none of them actually say where to implement such interface and what code the concrete method should contain!</p>