media: docs: add a cardlist for cx18 boards

There aren't many boards supported by this driver. So, add
a list for it manually generated.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/admin-guide/media/cardlist.rst

@@ -8,6 +8,7 @@ Cards List
 
 	au0828-cardlist
 	bttv-cardlist
+	cx18-cardlist
 	cx23885-cardlist
 	cx88-cardlist
 	em28xx-cardlist

Documentation/admin-guide/media/cx18-cardlist.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+CX18 cards list
+===============
+
+Those cards are supported by cx18 driver:
+
+- Hauppauge HVR-1600 (ESMT memory)
+- Hauppauge HVR-1600 (Samsung memory)
+- Compro VideoMate H900
+- Yuan MPC718 MiniPCI DVB-T/Analog
+- Conexant Raptor PAL/SECAM
+- Toshiba Qosmio DVB-T/Analog
+- Leadtek WinFast PVR2100
+- Leadtek WinFast DVR3100
+- GoTView PCI DVD3 Hybrid
+- Hauppauge HVR-1600 (s5h1411/tda18271)