Online documentation missing information about text padding in the book

[temyy]

Based on the conversation here, it would be good to add information on padding the text in Modonomicon's books in the online documentation

See https://github.com/klikli-dev/modonomicon/blob/b623bdcdebf3fba8c0a5f17fb725b300b70b120b/common/src/main/java/com/klikli_dev/modonomicon/api/datagen/book/BookModel.java#L51 and https://github.com/klikli-dev/modonomicon/blob/b623bdcdebf3fba8c0a5f17fb725b300b70b120b/forge/src/generated/resources/data/modonomicon/modonomicon/books/demo/book.json#L5