Use example.com subdomains instead of "real" domain names

[wenz]

The sample code is referring to "real" domain names such as alice.com, bob.com, and email.com. I would propose to change that to, say, alice.example.com, bob.example.com, and example.com to make crystal-clear that these really are examples. Just imagine one of those domains (especially the first two) gets cybersquatted.

I've filed (and fixed) a similar issue in the other repositories, here a sample (pun intended): DuendeSoftware/samples#209

[leastprivilege]

Thanks!