CameraNDK: add NDK API documents

This change adds document for ACameraManager, ACameraDevice and
ACameraCaptureSession.

Bug: 27102995

Change-Id: I5706337e419cd533c1c7d46e412dc62bf7c726cb
diff --git a/include/ndk/NdkImageReader.h b/include/ndk/NdkImageReader.h
index 041c378..9e7483d 100644
--- a/include/ndk/NdkImageReader.h
+++ b/include/ndk/NdkImageReader.h
@@ -14,6 +14,15 @@
  * limitations under the License.
  */
 
+/**
+ * @addtogroup Media Camera
+ * @{
+ */
+
+/**
+ * @file NdkImageReader.h
+ */
+
 /*
  * This file defines an NDK API.
  * Do not remove methods.
@@ -75,3 +84,5 @@
 #endif
 
 #endif //_NDK_IMAGE_READER_H
+
+/** @} */