Support for 64 Bit Integers Should be Added to Documentation for read_csv

[gmoore016]

readr appears to support reading 64 bit integers from CSVs out of the box if the col_type is set to "I".

This appears to be intentional given this issue was closed when the Vroom backend was added to readr and the vroom documentation lists "I" as an acceptable argument for col_type.

However, "I" is not currently listed as an acceptable type in the documentation for read_csv:

I'd suggest adding this to the docs, as it's not obvious and may drive people to uglier workarounds (like I was using before discovering the above).