Update model_usage to an enum

Closes #260 (closed)

docs/contents/workers/create.md

@@ -131,9 +131,9 @@ to get a basic structure for your worker.
 Cookiecutter will ask you for several options:
 
 `slug`
-: A slug for the worker. This should use lowercase alphanumeric characters or
-  underscores to meet the code formatting requirements that the template
-  automatically enforces via [black].
+: A slug for the worker. This should use lowercase alphanumeric characters,
+  underscores or hyphens to meet the code formatting requirements that the
+  template automatically enforces via [black].
 
 `name`
 : A name for the worker, purely used for display purposes.
@@ -159,6 +159,16 @@ Cookiecutter will ask you for several options:
 `email`
 : Your e-mail address. This will be used to contact you if any administrative need arise
 
+Cookiecutter will also automatically normalize your worker's `slug` in new parameters:
+
+`__package`
+: The name of the Python package for your worker, generated by normalizing the `slug`
+  with characters' lowering and replacing underscores with hyphens.
+
+`__module`
+: The name of the Python module for your worker, generated by normalizing the `slug`
+  with characters' lowering and replacing hyphens with underscores.
+
 ### Pushing to GitLab
 
 This section guides you through pushing the newly created worker from your
@@ -169,7 +179,7 @@ This section assumes you have Maintainer or Owner access to the GitLab project.
 #### To push to GitLab
 
 1. Enter the newly created directory, starting in `worker-` and ending with your
-   worker's slug.
+   worker's `slug`.
 
 2. Add your GitLab project as a Git remote: