[FEATURE] documentation of challenge-specific preprocessing requirements

[neuronflow]

@Astarakee and I discussed.

We should mention the necessary preprocessing steps and recommend the respective preprocessing function developed in #110 .

[MarcelRosier]

Do you have time to implement this @Astarakee or should i take over based on your notes?

[Astarakee]

Do you have time to implement this @Astarakee or should i take over based on your notes?
I will create the documentation soon (sorry that I missed that).