Add "Extend" documentation

- **If your Markdown files contain Emoji or other special Unicode**: Pandoc's Markdown-to-PDF converter uses LaTeX for elegant results, but sadly this also makes it quite bad at processing emoji.

- **If you want to use the Fachschaft Computerlinguistik styles**: Those are integrated in the Coliverter, so that every file converted with it also looks like it was produced by the Fachschaft.

- **If you want to generate certifications of commitment (“Engagementbescheinigungen”)**: Coliverter has templates, can sign them cryptographically etc.

- **If you want to generate commitment certifications (“Engagementbescheinigungen”)**: Coliverter has templates, can sign them cryptographically etc.

### Showcase

coliverter examples/basic_document.md examples/out/basic_document.pdf

```

If you want to generate a certification of commitment, you first need to create a JSON file containing all the required data. See the `examples/` folder for details. After that, it works just as expected:

If you want to generate a commitment certification, you first need to create a JSON file containing all the required data. See the `examples/` folder for details. After that, it works just as expected:

```bash

coliverter examples/certification_aktiver_fachschaftler.json Robby_McRobotface_Certification.pdf

```

## Extend

You can add new types of commitment certifications by completing the following steps:

1. Add a new class in the [`coliverter.certifications`](./src/coliverter/certifications) package.

2. Reference the class in [`coliverter.certifications.from_dict`](./src/coliverter/certifications/from_dict.py) in the `type ColiCertification` declaration (separated with `|`).

3. Add a new template in the [`coliverter.resources.templates.commitment_certification`](./src/coliverter/resources/templates/commitment_certification) package.

For more details, you can roughly follow the [documentation of Schwalbe PDF generator](https://gitlab.com/schwalbe-hd/pdf-generator/-/blob/master/docs/add_certification_type.md?ref_type=heads) (you will need to adapt paths, but other than that, the documentation should be mostly applicable to the Coliverter as well).

## Further reading

1. https://packaging.python.org/en/latest/tutorials/packaging-projects/