Make clear in the logs when the example app is ready

[bfabio]

The example app is ready after the message

[spid-express] info: samlCert expire in 12 months

and that's documented in the README.

We shouldn't need to document that with better logging, something along the lines of

[spid-express] Getting all metadata... (this can take a while)
and
[spid-express] Getting all metadata... done. App is ready at http://foobar