#avhack18 - update README to include use case, specs, etc.

README should include:

- Updated/clarified use cases and project objectives

- Actual specs of output formats. Even if we dont want to change them right now, docs can be more explicit WHAT is being created in output. E.g., the hardcoded ffmpeg command produces H.264 with these characteristics.

- Identify what the base ffmpeg command being concatenated (`$ffmpeg_vob_copy_string`) is achieving, and what it could drop with current config (goes back to overall use case and structure of source ISO)