rem: Scroll from Propierties of Container

Updated the corresponding documentation and ideas for how to realize
scrollable contents.

examples/container.zig

@@ -6,7 +6,7 @@ const Key = zterm.Key;
 
 const log = std.log.scoped(.example);
 
-pub const ExampleElement = struct {
+pub const ExampleElement = packed struct {
     pub fn element(this: *@This()) App.Element {
         return .{
             .ptr = this,