Document methods that are only supported on a specific Android version.

R=phensman@webrtc.org

Bug: webrtc:9819
Change-Id: Ifd3da9e1b70d0cfc479777c3a8031f632296be38
Reviewed-on: https://webrtc-review.googlesource.com/c/103680
Reviewed-by: Paulina Hensman <phensman@webrtc.org>
Commit-Queue: Sami Kalliomäki <sakal@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24987}
diff --git a/sdk/android/api/org/webrtc/ScreenCapturerAndroid.java b/sdk/android/api/org/webrtc/ScreenCapturerAndroid.java
index 2528460..fef28f5 100644
--- a/sdk/android/api/org/webrtc/ScreenCapturerAndroid.java
+++ b/sdk/android/api/org/webrtc/ScreenCapturerAndroid.java
@@ -31,6 +31,8 @@
  * place on the HandlerThread of the given {@code SurfaceTextureHelper}. When done with each frame,
  * the native code returns the buffer to the  {@code SurfaceTextureHelper} to be used for new
  * frames. At any time, at most one frame is being processed.
+ *
+ * @note This class is only supported on Android Lollipop and above.
  */
 @TargetApi(21)
 public class ScreenCapturerAndroid implements VideoCapturer, VideoSink {