Windows: Add step to verify Git Bash / MinGW / MSYS2 Setup

[karlhorky]

Git Bash uses MinGW and MSYS2 to emulate a Linux / Unix command line experience.

Some students have reported commands like ls not working after installing Git Bash:

david@DESKTOP-2021 MINGW64 /d/dokumente/github/next-ecommerce-store
$ ls
bash: ls: command not found

Let's add a step with 1-3 commands for verifying that all 3 of the following are installed correctly:

• Git Bash
• MinGW
• MSYS2

[karlhorky]

Seems like #32 (and the updated version #54) may have some of these things - so before implementing, check those first to see if those actually implement any of the 3 desired checks above.