build: document that aaudio was experimental

and make git blame point to a public description

NOTRY=true
BUG=webrtc:11947

Change-Id: Ic914c30243be8fd301140bc9d9489ff5869c6461
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/184502
Reviewed-by: Henrik Andreassson <henrika@webrtc.org>
Commit-Queue: Philipp Hancke <philipp.hancke@googlemail.com>
Cr-Commit-Position: refs/heads/master@{#32130}
diff --git a/webrtc.gni b/webrtc.gni
index a465f49..ba93242 100644
--- a/webrtc.gni
+++ b/webrtc.gni
@@ -120,8 +120,8 @@
   # Enable to use the Mozilla internal settings.
   build_with_mozilla = false
 
-  # Enable use of Android AAudio which requires Android SDK 26 or above and
-  # NDK r16 or above.
+  # Experimental: enable use of Android AAudio which requires Android SDK 26 or above
+  # and NDK r16 or above.
   rtc_enable_android_aaudio = false
 
   # Set to "func", "block", "edge" for coverage generation.