Broken images in README.md

[36degrees]

Hey 👋

There are two broken images in the README, both of which reference https://github.com/charity/tech-leads-study-group/images/homework.png.

This image doesn't appear to exist in the repo, and I don't think you can reference images like that on GitHub – I think the path would either need to be relative, or you'd need to reference it on raw.github.com.