Add comments to further clarify TemplateList code
Add comments to further clarify TemplateList code

In response to [^1][^2].

[^1]: https://github.com/alphagov/notifications-admin/pull/4263#discussion_r895762114
[^2]: https://github.com/alphagov/notifications-admin/pull/4263#discussion_r895791242

alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin