Update "Creating a Package" article with IncludeWorkflow operators

[banchan86]

Another way of creating Bonsai operators is to use the IncludeWorkflow operator. There is some documentation available at https://bonsai-rx.org/docs/api/Bonsai.Expressions.IncludeWorkflowBuilder.html and https://bonsai-rx.org/docs/articles/editor.html#workflow-extension but it might not be obvious to package developers. There are also related issues about how to package the resulting operators for distribution that could be documented.