If you are making a limited repository that will not have a ton of images, then you can get away with simply git tracking your images in the main repository.
With this setup, no further action is needed. For example, with a file structure of:
just use the image from README.bigb as:
which renders as:
However, if you are making a huge tutorial, which can have a huge undefined number of images (i.e. any scientific book), then you likely don't want to git track your images in the git repository.