Suggestion: Mention Linux shells, switch MS Win to PowerShell

When introducing the Terminal and shell for Mac users, explain that this is effectively identical to the shell environment used on Linux systems, so you are learning portable skills, not Apple-specific

On MS Windows, please switch to PowerShell! It’s been built-in since Windows 8, and is much much nicer to work with. The most common Bash commands work in PSH even without invoking the new Windows 10 subsystem for Linux.