docs: add table of contents to all Ecto pattern files

patterns/types.md

@@ -2,6 +2,15 @@
 
 Patterns extracted from Ecto's type system source code.
 
+## Contents
+
+1. [`use Ecto.Type` — The Four-Callback Custom Type](#1-use-ectotype--the-four-callback-custom-type)
+2. [`embed_as/1` — Controlling Embedded Serialization](#2-embed_as1--controlling-embedded-serialization)
+3. [`equal?/2` — Custom Equality for Change Detection](#3-equal2--custom-equality-for-change-detection)
+4. [`Ecto.Enum` — Constrained Atom Fields](#4-ectoenum--constrained-atom-fields)
+5. [`Ecto.ParameterizedType` — Types with Options](#5-ectoparameterizedtype--types-with-options)
+6. [Schemaless Types — `{data, types}` Changesets](#6-schemaless-types--data-types-changesets)
+
 ---
 
 ## 1. `use Ecto.Type` — The Four-Callback Custom Type