Improve documentation structure

Author: nyamsprod

docs/00-intro.md

@@ -57,6 +57,6 @@ composer require bakame/http-structured-fields
 - [Basic usage](01-basic-usage.md)
 - [Parsing and Serializing](02-parsing-serializing.md)
 - [Accessing The Field Values](03-field-values.md)
-- [Working with the Containers Data Type](04-containers.md)
+- [Working with The Containers](04-containers.md)
 - [Structured Field Validation](05-validation.md)
 - [Interacting with the PHP Ecosystem](07-extensions.md)

docs/04-containers.md

@@ -3,7 +3,7 @@ title: The Structured Field containers Data Types
 order: 5
 ---
 
-# Containers
+# Working with Structured Fields Containers
 
 While building or updating a Bare Item is straightforward, doing the same with the structured field containers
 requires a bit more logic. In the following sections we will explore how we can access, build and update