feat(docs): Add pointer to shields folder in new shield docs

docs/docs/development/new-shield.mdx

@@ -67,6 +67,10 @@ mkdir boards/shields/<keyboard_name>
 
 ## Base Kconfig Files
 
+:::tip[Example shields]
+You can check out the [`shields` folder](https://github.com/zmkfirmware/zmk/tree/main/app/boards/shields) in the ZMK repo that houses [the in-tree supported shields](../hardware.mdx) in order to copy and modify as a starting point.
+:::
+
 There are two required Kconfig files that need to be created for your new keyboard
 shield to get it picked up for ZMK, `Kconfig.shield` and `Kconfig.defconfig`.