minor fixes to doc

[git-girl]

What problem do you want to solve?

• there was a dead link in the doc
• there was an unnecessary cell from my understanding of the docs
  • While the cell does show that kinderfreibetraege are used in wohngeld the the rest of the documentation doesnt go into wohngeld at all. imo this isn't helpful in understanding kindergeld and more importantly distracting from the example.

also cool thanks for your work and having this be open source!

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 89.17%. Comparing base (6b6093d) to head (c4b785d).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #691 +/- ## ========================================== - Coverage 89.22% 89.17% -0.06% ========================================== Files 51 51 Lines 3592 3592 ========================================== - Hits 3205 3203 -2 - Misses 387 389 +2 ```

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[MImmesberger]

Yes, you're right. Thanks for spotting the mistakes and correcting them!

@lars-reimann Can you have a look where the CondaVerificationError in the readthedocs check comes from?

[MImmesberger]

@git-girl I included your changes in #695 to fix the issue with the readthedocs check. Thanks again!