Improve usability for github releases when no releases present

[paulmelnikow]

See #2785 #2017 and I seem to recall its coming up before, too.

1. We could change the error to no releases or repo not found.
2. We could add some documentation for the modal popup. It's kind of perfect for a badge-specific FAQ like this.

[sageworksstudio]

I believe number two is the better option (or a combination of both). It's not abundantly clear, at least for me it wasn't, that when you push a tag you're not also pushing a new release. New tags show up in the repository releases tab and even show up as a release count from the main repository page.

[erwanp]

It's not abundantly clear, at least for me it wasn't, that when you push a tag you're not also pushing a new release.

I support this!