docs: update intlify message ast

Author: kazupon

ARCHITECTURE.md

@@ -4,18 +4,22 @@
 
 The Message Syntax specification used in Vue I18n is defined [here](./spec/syntax.ebnf).
 
-## Intlify Message Syntax AST
+## Intlify Message AST structure
 
 ```mermaid
 flowchart TD
-  Resource
-  Plural
-  Message
-  Text
-  Named
-  List
-  Linked
-  LinkedKey
-  LinkedModifier
-  Literal
+  ResourceNode --> MessageNode
+  ResourceNode --> PluralNode
+  PluralNode --> MessageNode
+  MessageNode --> MessageElementNode
+  MessageElementNode --> TextNode
+  MessageElementNode --> NamedNode
+  MessageElementNode --> ListNode
+  MessageElementNode --> LiteralNode
+  MessageElementNode --> LinkedNode
+  LinkedNode --> LinkedModifierNode
+  LinkedNode --> LinkedKeyNode
+  LinkedNode --> NamedNode
+  LinkedNode --> ListNode
+  LinkedNode --> LiteralNode
 ```