Updated documentation.
diff --git a/docs/hazmat/primitives/index.rst b/docs/hazmat/primitives/index.rst
index 38ed24c..9121d15 100644
--- a/docs/hazmat/primitives/index.rst
+++ b/docs/hazmat/primitives/index.rst
@@ -14,3 +14,4 @@
     rsa
     constant-time
     interfaces
+    otp