build/*.csv are the data.
If you want to see in human-friendly format, column command will work good like below:
$ cat build/ap-northeast-1-multi-az.csv | column -s , -t
DB Instance Class Instance Type vCPU ECU Memory (GiB) PIOPS-Optimized Network Performance Price Per Hour
Micro instances db.t1.micro 1 Variable 0.615 - Very Low $0.060
Standard - Second Generation db.m3.medium 1 3 3.75 - Moderate $0.240
Standard - Second Generation db.m3.large 2 6.5 7.5 - Moderate $0.480
(snip)
csv/spec.csv is for specs, and csv/prices/*.csv are for prices. Update or add them for your need, and run rake to build joined files.
Original data are on https://aws.amazon.com/rds/pricing/ and https://aws.amazon.com/rds/details/ . Adding new data from their tables, you may need to clean up them manually, for example, removing asterisk, matching instance type names, and so on.