update README

README.md

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 # WGS SNPs calling pipeline for Paired-end Illumina sequencing
 ## From raw fastq data to vcf file.
 ## Pipeline features:
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        https://gatk.broadinstitute.org/hc/en-us/articles/360035890471-Hard-filtering-germline-short-variants
 
 
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-**Warning**
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+!! For the reference fasta file, he reference definition line must not contain space or special character.
 
-For the reference fasta file, he reference definition line must not contain space or special character.
-
-</div>
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 ## Snakemake features: fastq from csv file, config, modules, SLURM