Features/add esys docs

[MaGering]

Fixes #113

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

• All pre-commit tests passed locally with: pre-commit run -a
• File CHANGELOG.md was updated
• The docs were updated
  • [ ] 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

WARNING: When modifying use snakemake <=7.32.0, cf. #186

If data flow was adjusted:

• [ ] Data pipeline run finished successfully with: snakemake -jX

• [ ] Esys appdata was created successfully with: snakemake -jX make_esys_appdata

  (with X = desired number of cores, e.g. 1)

[MaGering]

First draft of esys documentation is ready for review. Let me know what you think @nesnoj

[nesnoj]

First draft of esys documentation is ready for review. Let me know what you think @nesnoj

Thanks a lot for this docs part! 🙏
I'll check ...