add a brief readme outlining test data types

README.md

@@ -1,3 +1,12 @@
 # oscar-test-data
 
-Test data for OSCaR breeding scheme calculator.
+Test data for [OSCaR](https://github.com/neuroinformatics-unit/OSCaR) breeding scheme calculator.
+
+All test data is fake, but matches the structure and edge cases of real data from a PyRAT server.
+
+## Types of test data
+
+- `*.json`: JSON files of raw PyRAT api responses
+- `pyrat-api-*.csv`: Expected csv files output by `get_pyrat_data`
+- `pyrat-data-*.csv`: Input csv files to `standardise_pyrat_csv`
+- `standardised-data-*.csv`: Expected output csv files from `standardise_pyrat_csv`