Update README.md

emphasis

README.md

@@ -33,7 +33,7 @@ wget https://farm.cse.ucdavis.edu/~ctbrown/sourmash-db/gtdb-rs214/gtdb-rs214-rep
 
 If you want to use a custom database, you will need to create a Sourmash sketch of your FASTA/FASTQ files of your reference database genomes (see [Sourmash documentation](https://sourmash.readthedocs.io/en/latest/) for details). In brief, this can be accomplished via the following:
 
-If you have a single FASTA file with one genome per record:
+If you have a single FASTA file with _one genome_ per record:
 ```bash
 sourmash sketch dna -f -p k=31,scaled=1000,abund --singleton <your multi-FASTA file> -o training_database.sig.zip
 ```