update README

README.md

@@ -22,5 +22,7 @@ $ choppy batch YaqingLiu/ngscheckmate_fastq-latest samples.csv -p Project [-l pr
 $ choppy query -L project:Label | grep "status"
 ```
 
+#### samples.csv
+The samples.csv contains at least 3 columns: sample_id, fastq1, fastq2.
 #### other parameters
 - subsampling_rate: The default subsampling rate is 1. The speed is not very slow.