Added documentation for HOTP implementation.
diff --git a/docs/index.rst b/docs/index.rst
index 176405b..7d6e618 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -75,6 +75,7 @@
     hazmat/primitives/index
     hazmat/backends/index
     hazmat/bindings/index
+    hazmat/oath/hotp
 
 The ``cryptography`` open source project
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