docs: record the clock trap, and confirm booting from internal storage

It boots from the internal drive with the stick removed — 18s to multi-user,
no failed units.

The first thing tried on it was `dnf install net-tools`, which failed with:

    Transaction failed: Rpm transaction failed.
      - systemd is needed by net-tools-2.0-0.77.20160912git.fc44.aarch64

systemd is obviously installed; the machine had just booted. The cause is the
clock. This machine's RTC cannot be set at all — ioctl(RTC_SET_TIME) returns
"No such device" — and reads 1970 every boot, so systemd advances it to its own
build date. That is close enough to look plausible and early enough that rpm
treats package signatures created after it as not yet valid, skips those
headers outright, and reports the packages as absent:

    Signature created at Sat Jul 25 18:33:30 2026 invalid: signature is not alive
    error: rpmdbNextIterator: skipping h# 282
    package systemd is not installed

chrony was already added to base.pkgs for the drift; it turns out to be load
bearing rather than a nicety, and it syncs within about five seconds of the
network appearing. Documented, because the symptom points nowhere near the
cause.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XWRjNJMistCy6ngXH5aJLS

README.md

@@ -133,9 +133,13 @@ Confirmed on hardware, from a USB stick:
 - The framebuffer console works (`simple-framebuffer`, 240x67)
 - The root filesystem mounts, systemd starts, and it reaches a login prompt
 - Networking works over a USB WiFi dongle, and sshd is reachable
-- `build/install-to-disk.sh` copies it onto the internal UFS
+- `build/install-to-disk.sh` copies it onto the internal UFS, and it boots from
+  there with the stick removed — 18s to multi-user, no failed units
 
-Not yet confirmed: booting from the internal drive rather than USB.
+The RTC cannot be set on this machine and reads 1970 at every boot, so `chrony`
+is installed and corrects the clock once the network is up. Until it does, rpm
+rejects package signatures dated after the (wrong) current time and reports
+installed packages as missing — see [docs/install.md](docs/install.md).
 
 Onboard WiFi does not appear at all, and audio, sensors, video decode and
 accelerated graphics are all absent — every one of them waiting on the