[StreamChatFlutter -> ConnectionStatusBuilder] Add docs

Signed-off-by: Sahil Kumar <xdsahil@gmail.com>

packages/flutter_widgets/lib/src/connection_status_builder.dart

@@ -2,6 +2,11 @@ import 'package:flutter/material.dart';
 import 'package:stream_chat_flutter_core/stream_chat_flutter_core.dart';
 import 'stream_chat.dart';
 
+/// Widget that builds itself based on the latest snapshot of interaction with
+/// a [Stream] of type [ConnectionStatus].
+///
+/// The widget will use the closest [Client.wsConnectionStatusStream] in case no
+/// stream is provided.
 class ConnectionStatusBuilder extends StatelessWidget {
   /// Creates a new ConnectionStatusBuilder
   const ConnectionStatusBuilder({