docs/home: Add 5G WWAN modem reference

Notes from bench-testing the Quectel RM500U-EA on tower, bought to
eventually replace stream's Virgin Media WAN. Like the switches and
APs, the module is configured out-of-band and is not referenced by
the flake.

Records what it takes to connect at all: the module must be switched
from its stock NCM composition to MBIM, since under NCM the PDP
context activates but the cdc_ncm link never raises carrier; and the
connect only succeeds with the network-expanded APN read off the
default-attach bearer, as IPv4.

Also flags the two consequences for stream: the SIM is CGNAT so it
cannot carry the public lease stream's WAN currently publishes, and
the bearer reports a /8 that would cover Tailscale's 100.64.0.0/10
if configured literally.

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

docs/sites/home/README.md

@@ -43,3 +43,9 @@ documented in [switches.md](switches.md).
 The Wi-Fi APs — `vibe` (MikroTik cAP ax) and `wave` (Cudy AX3000 on OpenWrt) — are dumb APs, also
 **not** managed by this flake. The shared VLAN-trunk design, SSIDs, per-AP management addressing,
 and the OpenWrt flash/config for `wave` are in [aps.md](aps.md).
+
+## 5G WWAN
+
+A Quectel RM500U-EA USB modem with a GoMo SIM is being evaluated as a replacement for `stream`'s
+Virgin Media WAN. It is bench-tested only and not yet referenced by the flake; the module settings
+it needs, the APN gotcha and the CGNAT consequences are in [wwan.md](wwan.md).