update README.md

Author: liuyanbioinfo

README.md

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 # IGV Viewer Web Application
 This project provides a web-based interface for visualizing BAM files using IGV.js. Users can view genomic data in an interactive IGV browser, specifying loci of interest for visualization.
 Input bam files should be accessible and valid in the app server. 
+![web_igv_viewer](app/static/img/web_igv_viewer.png)
 
 ## Features
 + **Interactive Genomic Visualization**: View genomic alignments and variations from BAM files directly in the browser using the IGV.js library.