DOC: add "Diagnosing performance bottlenecks" how-to and TOC entry

Username46786 · web-flow · commit 2c57a090aee0 · 2025-09-22T15:24:09.000-07:00
diff --git a/doc/source/user_guide/index.rst b/doc/source/user_guide/index.rst
@@ -90,3 +90,5 @@ Guides
     migration-3-strings
     gotchas
     cookbook
+    howto_performance_diagnosis
+
