text: Title: add inline examples to PythonCallable
  Body: https://docs.ploomber.io/en/latest/api/_modules/tasks/ploomber.tasks.PythonCallable.html#ploomber.tasks.PythonCallable
  
  * simple example with a couple of tasks and a few variations (one product, many products)
  * link to other relevant sections in the docs and other examples in projects