fix documentation

src/Levenshtein/__init__.py

@@ -140,7 +140,7 @@ def ratio(s1, s2, *, processor=None, score_cutoff=None):
     The indel distance calculates the minimum number of insertions and deletions
     required to change one sequence into the other.
     
-    This is calculated as ``1 - (indel / max(len1, len2))``
+    This is calculated as ``1 - (distance / (len1 + len2))``
 
     Parameters
     ----------