[CB-3905] Update Getting Started home page to focus on CLI.

- fill out getting started splash screen
- update splash screen to focus on CLI prereq, omit archaic CL utils
[CB-3926] Update references from x.y.z to x.x.x.

- convert hard-coded versions to x.x.x
- rewrite to suit
[CB-3816] Fix paths to screenshots in CLI guide.
[CB-3849] Expose new CLI guide on the homepage.