Find out a source of occupations

### Question to answer in this research

For the "Occupations" milestone we need a list of occupations and sectors. Sectors could be multi-level to be able link climate impacts and actions not for a single occupation only but for sectors or subsectors.

### Research reason

### Ideas to start with

- [ ] ...

Start by defining the occupations and sectors needed for the Occupations milestone, including whether sectors must be multi-level. Research and compare possible sources for these lists; done means a documented source and a sector structure suitable for linking climate impacts and actions.

Written by the indexing model from the issue text.