add t480 compatibility info (features)

Signed-off-by: Leah Rowe <info@minifree.org>

site/docs/install/t480.md

@@ -77,6 +77,33 @@ Official information about the T480 can be found here:\
 ...and information about the T480S can be found here:\
 <https://psref.lenovo.com/syspool/Sys/PDF/ThinkPad/ThinkPad_T480s/ThinkPad_T480s_Spec.pdf>
 
+What works in this port:
+-----------------------
+
+Intel graphics, internal screen, ethernet, USB, WLAN, HDA verbs (e.g. headphone
+jack), S3 suspend/resume, M2 NVMe SSDs and SATA, **all works perfectly**.
+External video outputs and webcam also work. Microphone works, line-out works...
+everything works. UART also available via line-out jack (jumpers required on
+the mainboard).
+
+The thunderbolt controller is currently unconfigured, so you can't use
+Thunderbolt, but the thunderbolt and regular USB-C connector can both be
+used for charging, and both can be used for video output (it shows up in xrandr
+as a DisplayPort). NOTE:
+<https://review.coreboot.org/c/coreboot/+/83274> is the patchset enabling
+Thunderbolt, but it currently breaks on S3 resume from sleep, so it's not
+included yet. This will be added to the Libreboot 20241205 release as a hotpatch
+when it's ready, and in the next testing release after Libreboot 20241205. This
+is true as of 5 December 2024.
+
+Backlight controls work, via software control (e.g. `xbacklight` utility), but
+the Fn keys for it don't currently work, as of 5 December 2024.
+
+Nvidia dGPU doesn't work and is disabled as of 5 December 2024; the Intel graphics
+are still available even on Nvidia models, so Intel graphics are used.
+
+WWAN slot untested.
+
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