add info on other package managers (besides just SDKMAN)

[SethTisue]

e.g., personally I install sbt and scala on MacOS using Homebrew

see discussion at #957 ; see also https://kotlinlang.org/docs/tutorials/command-line.html

[fineconstant]

@SethTisue Created pull request. Should we add info for some more package managers?

[ashawley]

There's a lot of pages with details about this on the other repo, see https://docs.scala-lang.org/getting-started-sbt-track/getting-started-with-scala-and-sbt-on-the-command-line.html

[ashawley]

These various "Getting started" pages are available from the home page, and from the Download page (arrows are original):

https://www.scala-lang.org/download/

[SethTisue]

leaving open because we're now well-stocked with MacOS info, but not other OS's