set homepage field more systematically

as an outsider to rust packager, i have noticed a handful of packages crossing new without a Homepage field in debian/control. Latest example is https://github.com/spytrap-org/spytrap-adb but there's actually a lot of those.

It would be great if rust packages would also have a Homepage field. I have come to understand (from #debian-rust) that this is actually a problem with the upstream crate, that doesn't detail a homepage field there in the first place, but I nevertheless feel there should be an extra effort made here to populate that field, if only a FTP site (ahaha, just kidding, i mean github project URL), which typically is available in debian/copyright (which is how I found the above URL).

capitol on IRC suggested the latter fallback, but it seems to me manual review and the possibility of a manual fallback would be good as well.