README: link BIOS flash guide, note renamable console account

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -28,6 +28,8 @@ over-the-air from this Gitea's container registry.
 The ISO installs **unattended** and bakes two users from
 [`iso-config.toml`](iso-config.toml): `parent` (admin/wheel) and `kid`
 (standard), both with a placeholder password to change on first login.
+The kid's account can be renamed post-install (see OPERATIONS.md) — the
+Big Picture autostart follows `CONSOLE_KID_USER` in `/etc/bc250-console.conf`.
 
 > ⚠️ The installer wipes the first disk with no prompts. Don't boot it on a
 > machine whose disk you care about.
@@ -40,6 +42,9 @@ The ISO installs **unattended** and bakes two users from
   games remotely, updates/rollback, GPU tuning, health checks
 - [`WIRING.md`](WIRING.md) — PSU/mains wiring, J1000 pinout, power-switch
   design (AC rocker + AUTO_PWRON), fans, first power-on
+- [`BIOS-FLASH.md`](BIOS-FLASH.md) — backup + flash the modded firmware via
+  the J4004 header, then the VRAM/IOMMU settings (ROMs are local-only, not
+  in this repo)
 
 ## Hardware prerequisites (on the board, not in the image)