add plantuml

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "plantuml.server":"http://www.plantuml.com/plantuml"
+}

test.md

@@ -1 +1,18 @@
-<h1>项目背景<h1>
+<h1>项目背景<h1>
+
+```plantuml
+@startuml  
+class User {  
+    +String name  
+    +String email  
+    +void login()  
+    +void logout()  
+}  
+
+class Admin {  
+    +void manageUsers()  
+}  
+
+User <|-- Admin  
+@enduml
+```