Fix typo [#9]

phylogenetic/rules/annotate_phylogeny.smk

@@ -1,6 +1,6 @@
 """
 This part of the workflow runs ancestral reconstruction and
-creates additonal annotations for the phylogenetic tree. It expects a
+creates additional annotations for the phylogenetic tree. It expects a
 single Newick tree and any additional files needed to create the
 annotations such as the aligned FASTA and metadata file.