Add documentation about working with lyrics data

[melaniewalsh]

Thanks so much for your work on this package! It's awesome.

I have 2 student groups who are working with this data for their final projects, and they were trying to figure out how to analyze the lyrics data included in taylor_album_songs, but they were getting stumped by the fact that the lyrics column contains nested data (shown below).

We figured out that you can unnest() the lyrics data, so that everything is included in the same dataframe, which is useful for basic text analysis (such as with tidytext).

taylor_df_with_lyrics <- taylor_album_songs %>% unnest(lyrics)

That was helpful for my students, so I thought it might be useful to include a couple of sentences in the documentation about the fact that the lyrics are nested, and maybe include an example of how users might unnest the data.

Thanks again!