poll: Add accidentally removed comments.

Fixes: #1808

Author: MritunjayTiwari14

lib/widgets/poll.dart

@@ -90,6 +90,10 @@ class _PollWidgetState extends State<PollWidget> {
           ConstrainedBox(
             constraints: const BoxConstraints(minWidth: 44, minHeight: 44),
             child: Padding(
+              // For accessibility, the touch target is padded to be larger
+              // than the vote count box.  Still, we avoid padding at the
+              // start because we want to align all the poll options to the
+              // surrounding messages.
               padding: const EdgeInsetsDirectional.only(
                 end: 5, top: verticalPadding, bottom: verticalPadding),
               child: Material(