Merge branch 'master-patch-c5d4' into 'master'

Update file phylo_exercise.md

See merge request !70

exercises/phylo_exercise.md

@@ -68,7 +68,7 @@
 
     ```
     # GENERATE A CORE SNP ALIGNMENT
-    snippy-core --prefix core [outdir] [outdir2] [outdir3]   
+    snippy-core --prefix core [outdir] [outdir2] [outdir3] --ref [reference]
     ```
 
     This command will give you various output, but among them is `core.aln` and `core.full.aln`. Both are fasta multiple sequence alignment, the first contains only the core SNPs, the other contains the full alignment of your reference and the samples inlcuding any invariant sites.