docs: add class diagram to README.md for Person, Student, and StudentShort classes

lab2/README.md

@@ -2,3 +2,50 @@
 
 > "И тут я обнаружил что случайно сделал 3-5 задачи в 1-2"
 
+## Диаграмма классов:
+
+```mermaid
+classDiagram
+    class Person {
+        +id: String
+        +git: String
+        -phone: String
+        -telegram: String
+        -email: String
+        +initialize(args: Hash)
+        +set_contacts(phone: String, telegram: String, email: String)
+        +git_present(): Boolean
+        +contact_present(): Boolean
+        +contact_info(): String
+        +valid_phone_number?(phone: String): Boolean
+        +valid_name?(name: String): Boolean
+        +valid_telegram?(telegram: String): Boolean
+        +valid_email?(email: String): Boolean
+        +valid_git?(git: String): Boolean
+    }
+
+    class Student {
+        +surname: String
+        +name: String
+        +patronymic: String
+        +initialize(args: Hash)
+        +from_string(student_string: String): Student
+        +read_from_txt(file_path: String): List~Student~
+        +write_to_txt(file_path: String, students: List~Student~)
+        +surname_and_initials(): String
+        +to_s(): String
+        +get_info(): String
+    }
+
+    class StudentShort {
+        +surname_initials: String
+        +contact: String
+        +initialize(student: Student)
+        +from_string(id: String, info_string: String): StudentShort
+    }
+
+    Person <|-- Student
+    Person <|-- StudentShort
+```
+
+где + - public, - - private