Documentation update on reading a file

[JakeZw]

When reading a file compressed into a zip file into a dataframe using the technique described herehttps://csv.juliadata.org/stable/examples.html#zip_example, once the last line in the code snippet below is executed, the first line needs to be re-executed. If we want to read a second file and go directly to the second line and then the third line again, we get an empty dataframe.

This should be documented somewhere.

`
z = ZipFile.Reader("a.zip") # or "a2.zip"

a_file_in_zip = filter(x->x.name == "a.csv", z.files)[1]

a_copy = CSV.File(a_file_in_zip) |> DataFrame
`