Documentation: Integration of FTP server with ASP.NET Core

[fubar-coder]

With 3.0 we're now able to use the ASP.NET Core infrastructure to host the FTP server. We need to create a documentation and a sample application.

• [x] Microsoft.Extensions.Hosting
  • [x] Documentation
  • [x] Example
• [x] ASP.NET Core
  • [x] Documentation
  • [ ] Example