arc-camera: add libcab and libcamera_v4l2_device in README.md

BUG=b:69015117
TEST=Manually with md_browser.py from the Chromium repo.

Change-Id: I898d98e190a84094f516210bffe2e37737e60c84
Reviewed-on: https://chromium-review.googlesource.com/1069947
Commit-Ready: Hung-yu Wu <hywu@chromium.org>
Tested-by: Hung-yu Wu <hywu@chromium.org>
Reviewed-by: Ricky Liang <jcliang@chromium.org>
diff --git a/README.md b/README.md
index c199510..8de74d1 100644
--- a/README.md
+++ b/README.md
@@ -71,6 +71,11 @@
   A package that installs all the necessary Android headers files required by
   the camera HAL.
 
+- `media-libs/cros-camera-libcab`
+
+  Provides functions to access the isolated camera 3A library if the camera HAL
+  requires it to work.
+
 - `media-libs/cros-camera-libcbm`
 
   A replacement for Android gralloc. The library provides [APIs](
@@ -85,6 +90,10 @@
 
   A port of the Android `libcamera_metadata`.
 
+- `media-libs/cros-camera-libcamera_v4l2_device`
+
+  Provides functions to access camera V4L2 devices.
+
 - `media-libs/libsync`
 
   A port of the Android `libsync`.