Add repo2docker logo to Jupyter design assets repo

[willingc]

Leaving this as a placeholder to check that we have provided a copy of this logo to the Jupyter design assets repo.

[manics]

Did anyone do this?

[choldgraf]

@manics I don't believe so. I believe that we still need to add the repo2docker logo here: https://github.com/jupyterhub/design

Another thing we could consider doing is creating a shared Figma board that any team member can access. That way we could more quickly create and share logos, rather than using a git repository for this.