Add custom README for published packages

[lightwalker-eth]

Background

A list of the images we're publishing to GitHub appear on the ENSNode repo homepage:

If we click on any of these, you'll see a README file is displayed.

Goal

Opening the details of any of the images we publish to GitHub should provide a simple readme file that's specifically tailored for the image.

Suggest keeping these tailored README files as simple as possible for right now. We should give a simple summary of the image and then link to other README files if someone wants more info.

Assumed Approach

I assume there's a way where we add some new .md files (not called README) into our repo and that we then update our Dockerfiles so that they copy / rename these files as needed to get them to appear as the README.md file on these published packages.