[Docs] Recursively clone qmk_firmware repo (#5378)

* Recursively clone qmk_firmware repo

Specifically, so that it grabs the submodules, since ARM keyboards are becoming more common, and we are seeing more issues about chibiOS not being downloaded (in the error log, rather than by question)

* Wrap in shell

docs/newbs_getting_started.md

@@ -66,8 +66,10 @@ You will need to install Git. It's very likely that you already have it, but if
 
 Once you have set up your Linux/Unix environment, you are ready to download QMK. We will do this by using Git to "clone" the QMK repository. Open a Terminal or MSYS2 MinGW window and leave it open for the remainder of this guide. Inside that window run these two commands:
 
-    git clone https://github.com/qmk/qmk_firmware.git
-    cd qmk_firmware
+```shell
+git clone --recurse-submodules https://github.com/qmk/qmk_firmware.git
+cd qmk_firmware
+```
 
 ?> If you already know [how to use GitHub](getting_started_github.md), we recommend that you create and clone your own fork instead. If you don't know what that means, you can safely ignore this message.