Crediting people/institutions not in github

**Is your feature request related to a problem? Please describe.**
I would like to credit an organisation for providing some open data in which my project is based, but that organisation does not have a github user (although in my particular case, it does have a github group -but that may not be as common).

I attempted to do so here: https://github.com/ccamara/osm_imports_preparations/issues/4, but unfortunately, when using the bot, I got the following answer:

> I couldn't determine any contributions to add, did you specify any contributions?
> Please make sure to use valid contribution names.

**Describe the solution you'd like**
Add contributors that do not have a github account in a similar way:

If they are a github group:
- Display group's name, link and avatar, as a regular user

If they do not have a github account, it would be nice to pass name, email, url and avatar as parameters. Avatar may be obtained from gravatar too.