update README

README.md

@@ -15,7 +15,16 @@
        https://gatkforums.broadinstitute.org/gatk/discussion/2806/howto-apply-hard-filters-to-a-call-set
        https://gatk.broadinstitute.org/hc/en-us/articles/360035890471-Hard-filtering-germline-short-variants
 
-_**Warning:** For the reference fasta file, he reference definition line must not contain space or special character._
+
+<div class="panel panel-warning">
+**Warning**
+{: .panel-heading}
+<div class="panel-body">
+
+For the reference fasta file, he reference definition line must not contain space or special character.
+
+</div>
+</div>
 
 
 ## Snakemake features: fastq from csv file, config, modules, SLURM