title: How to add .dcproj into solution via dotnet sdk
body: <p>I have a solution named: <code>MyProject.sln</code> and project related to docker called - <code>docker-compose.dcproj</code>.</p>
  
  <p>I want to create dotnet new template which will contain support for docker-compose through project <code>docker-compose.dcproj</code>.</p>
  
  <p>I tried this command:</p>
  
  <p><code>dotnet sln MyProject.sln add docker-compose.dcproj</code></p>
  
  <p>I got this error message:</p>
  
  <blockquote>
    <p>Project 'C:\MyProject\docker-compose.dcproj' has an unknown project type and cannot be added to the solution file. Contact your SDK provider for support.</p>
  </blockquote>
  
  <p>I am using <code>.net core sdk</code> version <code>3.1.100</code>.</p>
  
  <p>How to add <code>docker-compose.dcproj</code> into solution via command above?</p>