Add an emphasis on QMK MSYS terminal (qmk#21168)

* Add an emphasis on QMK MSYS terminal

Not using MSYS terminal is a frequent user error. This change
adds an additional statement to guide users to run the first
command in MSYS itself. Edited the same statement for consistency
in the other OSes.

* Update instructions for the other operating systems

docs/newbs_getting_started.md

@@ -120,23 +120,23 @@ NOTE: remember to follow the instructions printed at the end of installation (us
 
 ### ** Windows **
 
-After installing QMK you can set it up with this command:
+Open QMK MSYS and run the following command:
 
     qmk setup
 
 In most situations you will want to answer `y` to all of the prompts.
 
 ### ** macOS **
 
-After installing QMK you can set it up with this command:
+Open Terminal and run the following command:
 
     qmk setup
 
 In most situations you will want to answer `y` to all of the prompts.
 
 ### ** Linux/WSL **
 
-After installing QMK you can set it up with this command:
+Open your preferred terminal app and run the following command:
 
     qmk setup
 
@@ -150,7 +150,7 @@ Luckily, the fix is easy. Run this as your user: `echo 'PATH="$HOME/.local/bin:$
 
 ###  ** FreeBSD **
 
-After installing QMK you can set it up with this command:
+Open your preferred terminal app and run the following command:
 
     qmk setup