Cannot use read_psd from S3_WRITE

[achafetz]

By default, the bucket for reading in a file using read_psd is from the S3_READ bucket.

gophr/R/read_psd.R

Lines 84 to 86 in 1dfa65b

	"pdap" = aws.s3::s3read_using(handle_psd_format,
	bucket = Sys.getenv("S3_READ"),
	object = file))

This could be a param, but ideally we want the user to be able to run the same code on their local machine or in Workbench. To do so, we need a sub function build into read_psd that checks if the PSD exists in S3_READ and if not, checks for it in S3_WRITE.