AAudio: add group in headers for doxygen

This is needed for proper navigation in the NDK reference docs.

Bug: 36995264
Test: Look at NDK docs after staging. Audio link should work.
Change-Id: Ifb61f95d536310a420d90f32c64557b75901d751
Signed-off-by: Phil Burk <philburk@google.com>
diff --git a/media/libaaudio/include/aaudio/AAudio.h b/media/libaaudio/include/aaudio/AAudio.h
index 921248a..551dcc9 100644
--- a/media/libaaudio/include/aaudio/AAudio.h
+++ b/media/libaaudio/include/aaudio/AAudio.h
@@ -15,7 +15,16 @@
  */
 
 /**
- * This is the 'C' ABI for AAudio.
+ * @addtogroup Audio
+ * @{
+ */
+
+/**
+ * @file AAudio.h
+ */
+
+/**
+ * This is the 'C' API for AAudio.
  */
 #ifndef AAUDIO_AAUDIO_H
 #define AAUDIO_AAUDIO_H
@@ -525,3 +534,5 @@
 #endif
 
 #endif //AAUDIO_AAUDIO_H
+
+/** @} */