Update docs for bad ini syntax in noreply

[kdumontnu]

Small nit, but the example used in app.example.ini for NO_REPLY_ADDRESS will cause gitea to error with:

models/avatar.go:72:LibravatarURL() [E] LibravatarService.FromEmail(email=user@noreply.%(domain)s): error mail: expected single address, got "s"

Ini only supports recursive values in For all value of keys, there is a special syntax %(<name>)s, where <name> is the key name in same section or default section

Note: I've added an upstream feature request to allow ini to reference values from other sections.