archetypes/maven-archetype-dotnet-simple/src/main/resources/META-INF/archetype.xml

<archetype>
  <id>maven-archetype-dotnet-simple</id>
  <resources>
    <resource>src/main/csharp/Sample/MyApp.cs</resource>
    <resource>src/test/csharp/Sample/MyAppTest.cs</resource>    
  </resources>
</archetype>