I think this product is not open source
This product is not open source. It can not be used in production. You will not be able to add custom types and custom workflows. :(
A message like
It can only be used for development and will be stopped if used in production means that you are using Nuxeo-provided prepackaged hotfixes, which are a paid service. You must uninstall the prepackaged hotfixes if you don't have a support contract and therefore a valid license (instance.clid) file.
Otherwise you can always compile everything from source. But not use our prepackaged hotfixes directly.
The full source of Nuxeo is available at https://github.com/nuxeo, under an open source license (see https://doc.nuxeo.com/nxdoc/licenses).
you can create a doctype with simple XML contributions using org.nuxeo.ecm.core.schema.TypeService extension points (schema and doctype)