Add "data schema generation" guide for KDF plugin

[AndreiKingsley]

1. Show how to use https://kotlin.github.io/dataframe/dataschemagenerationmethods.html methods for this.
2. Add 2 possible options:

• by running main with schema printing
• by adding project dependency in KTNB and copy-paste cell output with schema

[AndreiKingsley]

Probably here: https://kotlin.github.io/dataframe/dataschema.html#schemas-for-nested-structures