[WIP] Add initial logos for Physiome Project

[Copilot]

Thanks for asking me to work on this. I will get started on it and keep this PR's description up to date as I form a plan and make progress.

Original prompt

I want to create a repository that will contain logo / icon image files related to the Physiome Project. Initially there will be the logo for the Physiome Model Repository and CellML, but over time we intend to use this as a repository to archive relevant logos for ease of discovery and reuse. I want to use CC0 as the license to ensure unrestricted reusability of the contained image files.