Add info regarding Channel ID for ijo42-latest as per https://github.com/ijo42/CurseForge2Discord/issues/5#issuecomment-766320609

- Example for tracking multiple Curseforge projects

- Re-implemented check for GitHub related variables in 30-config
- Added check whether GITHUB_TOKEN is set to run

- Made changing bot version in Dockerfile easier

Did I really just made the & instead of $ typo and then copy paste it throughout the whole config file? Why yes, yes I did.

- Include environment variables in README
- Add file ownership change to 30-config to ensure bot.conf is always owned by PUID:PGID