Fix missing rule on destructors

ehuss · ehuss · commit 52499e60f338 · 2025-06-15T17:05:06.000-07:00
To stay consistent with the rest of the book, the chapter head gets a
rule label.
diff --git a/src/destructors.md b/src/destructors.md
@@ -1,3 +1,4 @@
+r[destructors]
 # Destructors
 
 r[destructors.intro]
