Not sure if there are any restrictions keeping you from linking directly from the project readme, but perhaps a separate repo can drive: https://pages.github.com/
Some months ago, before a GitHub update, you could just paste an image while editing a Markdown file and it would be uploaded to their CDN. You could use that link even in other files (e.g. Org files in my case). They changed their upload system and this is not the case anymore.