#157 emissions data and readme

[dvdstrzl]

Extend dataset readme for emissions #157

Before merging into dev-branch, please make sure that the following points are checked:

• [X] All pre-commit tests passed locally with: pre-commit run -a ~- [ ] File CHANGELOG.md was updated~
• [X] The docs were updated
  • [X] if dataset.mds were updated, the dataset docs were regenerated using python docs/generate_dataset_mds.py

If packages were modified: ~- [ ] File poetry.lock was updated with: poetry lock~ ~- [ ] A new env was successfully set up~

If data flow was adjusted: ~- [ ] Data pipeline run finished successfully with: snakemake -jX~ ~- [ ] Esys appdata was created successfully with: snakemake -jX make_esys_appdata~

[nesnoj]

@aaronschilling @dvdstrzl, you mentioned that sth. might be missing - is this completed now? And please resolve the merge conflict (or drop me a note if you need support with this)