Add support for CSV in slug CLI parameter #28
Description
When someone want to ZIM multiple slugs, it is currently possible to do this with multiple slug parameters, e.g. --slug lua --slug gcc.
Zimfarm is however not (yet?) capable to create such commands (UI is not ready and complex to develop - needs add and remove buttons for a single flag), backend is not ready but probably easier to do)
When we need to pass multiple values like this, we currently rely on scraper code which accepts to have a CSV value like --slug lua,gcc, and then split this value.
Devdocs scrapper should support this as well (not urgent at all however since we do not expect to use this a lot in first Zimfarm recipes).