Add an overview of workshops making use of this lesson

In some other Carpentries lessons we keep an overview of workshops using the lesson [in a markdown file in the root of the repository](https://github.com/carpentries-incubator/deep-learning-intro/blob/main/workshops.md) and stimulate keeping this updated in the README (see [this PR](https://github.com/carpentries-incubator/lesson-gpu-programming/pull/114/files)).

This is in addition to the registration of workshops at https://carpentries-incubator.org/ (that is unfortunately often not filled in). An alternative would be to promote filling in this registration form in the README of this lesson.