Document emacs use, both inside and outside the devcontainer. (rough instructions in ticket)

[jwhitlark]

Running emacs inside the devcontainer (locally, on docker):

• install https://github.com/devcontainers/cli locally
• add emacs-nox to the devcontainer docker file
• devcontainer up --workspace-folder .
• devcontainer exec --workspace-folder . emacs ?

Running emacs locally and connecting to a repl started in the project.

• install https://github.com/devcontainers/cli locally
• Should be able to start the repl as a postStartCommand in devcontainer.json
• Local edits should propagate to the container.
• Expose the repl port locally via forwardPorts in devcontainer.json
• devcontainer up --workspace-folder .
• Run emacs locally and connect to your repl.

Check this blog post for a slightly different way to do it. Might be better?