[LLC, Persistence] Add doc comments

Signed-off-by: Sahil Kumar <[email protected]>

packages/stream_chat_persistence/lib/src/entity/reads.dart

@@ -1,14 +1,19 @@
 import 'package:moor/moor.dart';
 
+/// Represents a [Reads] table in [MoorChatDatabase].
 @DataClassName('ReadEntity')
 class Reads extends Table {
+  /// Date of the read event
   DateTimeColumn get lastRead => dateTime()();
 
+  /// Id of the User who sent the event
   TextColumn get userId => text()();
 
+  /// The channel cid of which this read belongs
   TextColumn get channelCid =>
       text().customConstraint('REFERENCES channels(cid) ON DELETE CASCADE')();
 
+  /// Number of unread messages
   IntColumn get unreadMessages => integer().nullable()();
 
   @override