Making :confirmable the default behavior

Hey all
Just did a fresh install of devise_token_auth and ran into a couple issues. The one I wanna address here is that by default, the user model was created with `:confirmable` in the User model commented out. Additionally in the configuration guide, there is no mention of uncommenting or using the `:confirmable` keyword in the User model. I propose that we make the model confirmable by default. Since the majority of the use cases (to my knowledge) would involve email confirmation. Barring that, I suggest we at least mention the uncommenting of the `:confirmable` keyword in the user model as a part of the [Email Authentication](https://devise-token-auth.gitbook.io/devise-token-auth/config/email_auth) configuration section.

Happy to write up a PR if folks think this is valuable
Thanks

Start by inspecting the generated User model and the Email Authentication configuration guide linked in the issue. Compare the current commented :confirmable setup with the requested default behavior, then clarify whether the goal is a behavioral change or documentation update. Done means the chosen approach is reflected consistently in the generator and guide, with relevant verification added if the repository identifies it.

Written by the indexing model from the issue text.