Highlight the hint about qmk doctor

Co-authored-by: Drashna Jaelre <drashna@live.com>

docs/newbs_flashing.md

@@ -108,7 +108,7 @@ However, this does rely on the bootloader being set by the keyboard. If this inf
 
 In this case, you'll have to fall back on specifying the bootloader. See the [Flashing Firmware](flashing.md) Guide for more details.
 
-If your bootloader is not detected by `qmk flash`, try running `qmk doctor` for suggestions on how to fix common problems.
+!> If your bootloader is not detected by `qmk flash`, try running `qmk doctor` for suggestions on how to fix common problems.
 
 ## Test It Out!