Update README.md

corrections. For scATAC-seq data with multiple read and barcode files, you can

use "," to concatenate multiple input files as the example [above](#general). 

The BED format (fragment file) for bulk and single-cell are different except for the first

three columns. For bulk data, the columns are "chrom chrom_start chrom_end N mapq strand".

For single-cell data, the columns are "chrom chrom_start chrom_end barcode duplicate_count" 

The BED format (fragment file) for bulk and single-cell is different except for the first

three columns. For bulk data, the columns are

    chrom chrom_start chrom_end N mapq strand

For single-cell data, the columns are 

    chrom chrom_start chrom_end barcode duplicate_count

as the definition of the fragment file in 

[CellRanger](https://support.10xgenomics.com/single-cell-atac/software/pipelines/latest/output/fragments). 

Note that chrom_end is open-end.