update README.md

README.md

@@ -11,7 +11,7 @@ Bam file(s) should be properly sorted, and the probe file (bed file) and the out
     choppy batch YaqingLiu/bamdst-latest samples.csv -p project_name
 
 -**samples.csv**
-    sample_id,sample,bam,bed
+    sample_id,sample,bam,bai,bed
 
 -**bamdst normal usage:**
     bamdst -p <probe.bed> -o ./ in1.bam