Revamp README: restructure docs and features

Trim and reorganize README.md: remove large inline documentation (installation steps, full feature/CSS/API details) and replace with concise Quick Start, Installation steps, feature highlights, and direct links to the hosted documentation site. Minor formatting fixes (badge/newlines, video tag) and emphasize File Transformation plugin and Jellyfin 10.11+ requirement. This centralizes long-form docs on the external docs site and simplifies the repository README for quicker onboarding.

Author: n00bcodr