docs: Italicize book title in README · tidyverse/duckplyr@ab5b621

declared S3 method 'groups.duckplyr_df' not found

`df_from_csv()` was deprecated in duckplyr 1.0.0.

`df_from_file()` was deprecated in duckplyr 1.0.0.

`duckplyr_df_from_csv()` was deprecated in duckplyr 1.0.0.

`df_to_parquet()` was deprecated in duckplyr 1.0.0.

`as_duckplyr_df()` was deprecated in duckplyr 1.0.0.

`duckplyr_df_from_parquet()` was deprecated in duckplyr 1.0.0.

`duckplyr_execute()` was deprecated in duckplyr 1.0.0.

`is_duckplyr_df()` was deprecated in duckplyr 1.0.0.

`as_duckplyr_tibble()` was deprecated in duckplyr 1.0.0.

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