Upgrade Part I, Introduction and bsdinstall chapters

• Upgrade Part I to indicate that this part of the handbook covers Wayland too
• Introduction chapter:
  • Improvements in FreeBSD history
  • References to Wayland
  • Remove companies from Who uses FreeBSD section, let this task to the FreeBSD Foundation
  • Upgrade offline paths for Handbook and FAQ
  • Use https in links
  • Minor typos
• bsdinstall chapter:
  • Upgrade synopsis section
  • Upgrade install chapter with last changes in the installer
  • Upgrade stale images
  • Add alt text to images
  • Remove references to specific versions

Reviewed by: bcr@, arrowd@, jrm@, karels@, mckusick@