Changes to this template & Curriculum Development Handbook

We have made a few changes to this template, primarily motivated by the release of the [Curriculum Development Handbook](https://carpentries.github.io/curriculum-development/) which replaces the former section on [Lesson Design](https://github.com/carpentries/lesson-example/blob/651eeddd99910a3b713ba593b87b15770ef81c16/_episodes/01-design.md).

This allows us to separate out curriculum development and lesson template development. As the CDH is being released as a first draft, feedback on how it affects this lesson template is welcome in this issue.

Start by comparing the lesson template with the Curriculum Development Handbook and the former _episodes/01-design.md lesson-design section linked in the issue. The issue requests feedback on how the handbook affects the template, but it does not define a specific change or completion criterion.

Written by the indexing model from the issue text.