Docs/mb/lenovo/t420: List working, tested and non-working features

Signed-off-by: Piotr Szymaniak <szarpaj@grubelek.pl>
Change-Id: I6fb4a8da44125b4280d37d0cf7c372f8024fb2d1
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51952
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
diff --git a/Documentation/mainboard/lenovo/t420.md b/Documentation/mainboard/lenovo/t420.md
index 00ce45f..189649b 100644
--- a/Documentation/mainboard/lenovo/t420.md
+++ b/Documentation/mainboard/lenovo/t420.md
@@ -18,6 +18,40 @@
 
 Steps to access the flash IC are described here [T4xx series].
 
+## Working
+ * CPU: Sandy Bridge i5-2520M, i7-2670QM
+ * RAM module combinations of 2G+0, 2G+2G, 4G+0
+ * mSATA
+ * USB
+ * Video (Intel integrated)
+ * Sound (integrated speakers, integrated mic, external headphones, external mic)
+ * LAN
+ * Mini-PCIe slots (WLAN)
+ * Bluetooth
+ * Linux
+ * Windows 10 (through SeaBIOS as payload, using a VGA BIOS)
+ * DVD-ROM drive
+ * SD card slot
+ * TrackPoint
+ * Touchpad
+ * Webcam
+ * Fn hotkeys (backlight control, thinklight)
+ * Thinklight
+ * Mute button (Speaker only)
+ * Mini Jack audio (headphones)
+ * Suspend (Linux)
+
+## Not tested
+ * DSub (VGA) out
+ * DisplayPort out
+ * eSATA
+ * ExpressCard
+ * WWAN
+
+## Not working/TODOs
+ * Mutemic button doesn't mute
+ * Suspend (Windows 10)
+
 [T4xx series]: t4xx_series.md
 [flashing tutorial]: ../../flash_tutorial/ext_power.md
 [T420 / T520 / X220 / T420s / W520 common]: Sandy_Bridge_series.md