Add new images and favicon for site documentation

- Added favicon.ico for site branding.
- Included various images for documentation, including:
  - bios-secure-boot-disabled.png
  - check-torproject-confirmation.png
  - desktop.png
  - keepassxc-create-wizard.png
  - kleopatra-keygen.png
  - mac-boot-picker-usb.png
  - pai-desktop images
  - thunar-encrypt-menu.png
  - utm images
  - waybar-tor-indicator.png
- Added logo.png for site branding.

Author: nirholas