A-UserGuide

Set up product website and add User Guide

- Added a representative screenshot of ElenaBot GUI as docs/Ui.png.
  - Shows full GUI window with product name in title bar.
  - Single-window screenshot; not stitched.
- Added a brief User Guide in docs/README.md.
  - Uses GitHub Flavored Markdown (GFMD).
  - Instructions for enabling GitHub Pages included.
  - Covers basic chatbot usage, features, and navigation.