docs: add small section about TraceSource and trace helpers
diff --git a/docs/source/index.rst b/docs/source/index.rst
index b763bc1..22a788e 100644
--- a/docs/source/index.rst
+++ b/docs/source/index.rst
@@ -14,4 +14,5 @@
    fw
    applications
    examples
+   metric
    faq