Add style guide for docker image

All docker images are to have a baseline commonality:
- tmux, nvim, helix and PowerShell installed and configured.
- Configurations are called from etc/bashrc, including aliases.
- New bash libraries are added to /bin/bash
- README houses gif showing login, print language versions, relevant environment variables
- this gif is updated in the appropriate readme with relevant releases via GitHub actions or similar
- automated testing to validate these things