Add a lot more to the Downloads page in regards to Installation

There should be a canonical way to install and upgrade rakudo star.

Have separate headings for each major platform
- Mac section should discuss homebrew and whether that is a recommended method
- Explain where things are installed and how to add them to your path
Do not include rakudobrew if it continues to be fiddly
Modern languages almost require a package manager of some sort. Include explanation / link to zef on this page?
Most of all, assume that the user is a beginner

Raku / user-experience