datayeet: warn about lost miis

Mii data gets reset by initial setup, add warning to back it up (maybe script this one day)

Author: lilyuwuu

docs/_include/ctrnand-datayeet.md

@@ -1,5 +1,11 @@
 This section will reset your system settings to its defaults. **Installed games and their save data will not be affected.** This is **required** to prevent known issues relating to extended memory mode and applets on some consoles.
 
+::: warning
+
+This process will reset your Mii data. If you wish to save any Miis that you have created, either [generate a QR code](https://en-americas-support.nintendo.com/app/answers/detail/a_id/298/~/how-to-generate-a-qr-code%E2%84%A2-for-a-mii) for each Mii that you want to save, or make a backup of `SYSNAND CTRNAND:/data/<ID0>/extdata/00048000/f000000b` before following these instructions. You can restore this file to the same directory *after* your console has gone through initial setup.
+
+:::
+
 1. Power off your console
 1. Press and hold (Start), and while holding (Start), power on your console. This will launch GodMode9
 1. Navigate to `[0:] SDCARD` -> `gm9` -> `in`