doc: emphasize usage of MSYS2 MSYS Shell
doc: emphasize usage of MSYS2 MSYS Shell

Some users started the wrong shell (MinGW) and ended up having build
issues, added a note about starting the right shell.

Jira: ZEP-2004
Signed-off-by: Anas Nashif <0d9952ec84ac43c159f6b7e7ed99a9080c00dd6e@intel.com>

bigdinotech/zephyr,bigdinotech/zephyr,bigdinotech/zephyr,bigdinotech/zephyr,bigdinotech/zephyr