update readme

Author: nh13

README.md

@@ -80,6 +80,7 @@ An observed barcode matches an expected barcode if all the following are true:
    mismatches (see `--max-mismatches`).
 2. The difference between number of mismatches in the best and second best barcodes is greater
    than or equal to the minimum mismatch delta (`--min-mismatch-delta`).
+
 The expected barcode sequence may contains Ns, which are not counted as mismatches regardless
 of the observed base (e.g. the expected barcode `AAN` will have zero mismatches relative to
 both the observed barcodes `AAA` and `AAN`).