Update .workflow-index.yml

.workflow-index.yml

+language: Snakemake
+name: Single end metaphlan2 workflow
+description: Single end metaphlan2 workflow
+url: https://gitlab.pasteur.fr/metagenomics/snakemake/blob/master/workflows/metaphlan2/single_metaphlan2/Snakefile
+categories: [Metagenomics]
+authors:
+  - firstname: Kenzo-Hugo
+    lastname: Hillion
+    email: kenzo-hugo.hillion1@pasteur.fr