added ui cookbook audio indicator docs

docusaurus/docs/Flutter/06-ui-cookbook/07-audio-volume-indicator.mdx

@@ -0,0 +1,50 @@
+# Audio Volume Indicator
+
+The audio indicator provides visual feedback when a user connected to the call is speaking.
+
+You can observe several things about audio in the `CallParticipantState` class such as:
+
+* Check if the current user is the dominant speaker: `participantState.isDominantSpeaker`
+* Check if the current user is speaking: `participantState.isSpeaking`
+* Check the audio level of the user: `participantState.audioLevel`
+
+## Customising the audio volume indicator
+
+You can change the color of the audio indicator using the `audioLevelIndicatorColor` parameter of the `StreamCallParticipant` widget:
+
+```dart
+StreamCallContainer(
+  // ...
+  callContentBuilder: (
+    BuildContext context,
+    Call call,
+    CallState callState,
+  ) {
+    return StreamCallContent(
+      call: call,
+      callState: callState,
+      callParticipantsBuilder: (
+        BuildContext context,
+        Call call,
+        CallState callState,
+      ) {
+        return StreamCallParticipants(
+          call: call,
+          participants: callState.callParticipants,
+          callParticipantBuilder: (
+            BuildContext context,
+            Call call,
+            CallParticipantState participantState,
+          ) {
+            return StreamCallParticipant(
+              call: call,
+              participant: participantState,
+              audioLevelIndicatorColor: Colors.teal,
+            );
+          },
+        );
+      },
+    );
+  },
+),
+```