Add note on comparing schemas to README

README.md

@@ -204,6 +204,11 @@ In order to save to S3 you must have valid access credentials stored in
 `~/.aws`. We do not currently allow you to specify an alternate storage
 location.
 
+**NOTE:** The schemas should be kept in sync with the exception of
+output-specific columns (e.g., `instance_id` in the S3 output). You can compare
+the two schemas by running
+`diff -y automation/schema.sql automation/DataAggregator/parquet_schema.py`.
+
 Browser and Platform Configuration
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