Add example of a proc_macro_attribute
diff --git a/examples/README.md b/examples/README.md
index 08ca7a1..75bc450 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -21,3 +21,8 @@
An example of parsing a custom syntax within a `functionlike!(...)` procedural
macro. Demonstrates how to trigger custom warnings and error messages on
individual tokens of the input.
+
+### [`trace-var`](trace-var)
+
+An attribute procedural macro that uses a syntax tree traversal to transform
+certain syntax tree nodes in a function body.