docs: increase TOC depth

kenjis · kenjis · commit 17692315f650 · 2023-03-24T10:41:16.000+09:00
diff --git a/user_guide_src/source/libraries/email.rst b/user_guide_src/source/libraries/email.rst
@@ -18,7 +18,7 @@ CodeIgniter's robust Email Class supports the following features:
 
 .. contents::
     :local:
-    :depth: 2
+    :depth: 3
 
 ***********************
 Using the Email Library
