New Section: Dockerfile ENTRYPOINT and CMD

[ivorscott]

Fixes issue #90

Section: ENTRYPOINT and/vs CMD

• [ ] Lecture 1 basic info, no examples
• [ ] Lecture 2 Entrypoint for CLI with example
• [ ] Assignment 1 Entrypoint for curl cli
• [ ] Lecture 3 Entrypoint for pre-CMD scripts with example
• [ ] Lecture 4 Entrypoints in official images for script automation
• [ ] Assignment 2 Entrypoint for react app with env var for API_URL
• [ ] Quiz

[BretFisher]

@ivorscott I updated the OP to reflect the new flow and lecture subjects