Allowed values missing in docs

[dbrgn]

In the docs (https://spaceapi.io/pages/docs.html), enum values are not listed. E.g. for issue_report_channels, the allowed values are not shown.

JSON schema can be found here: https://github.com/SpaceApi/schema/blob/master/13.json

This must be fixed in https://github.com/SpaceAPI/website/blob/master/generate_api_docs.py.