Ticket: Add missing environment variable info to README

[mcvholloway]

When running the project locally, some required environment variables (like VITE_COURSE_NAME, VITE_PROXY_DOMAIN, etc.) are not documented in the README. As a result, the dev server produces broken URLs (/undefined) and a blank page.

It would be helpful to update the README with these variables so that the project can be run without issues.