AppVeyor doesn't require an appveyor.yml in the repos (in fact it has
some limitations as noted in comments below), but doing so has two great
advantages over the web UI:

- appveyor.yml can be revisioned together with the code, so instructions
  should always be in synch with the code

- appveyor.yml can be reused for people's private repositories (be on
  fdo or GitHub, etc.)

Acked-by: Roland Scheidegger <sroland@vmware.com>