docs(readme/class-diagram): rule and tag relationship (#342)

Author: binhtran432k

README.md

@@ -255,6 +255,7 @@ classDiagram
     Feature "1" *-- "0..1" Background: background
     Scenario --|> ScenarioDefinition
     Tag "0..*" --* "1" Feature: tags
+    Tag "0..*" --* "1" Rule: tags
     Tag "0..*" --* "1" Scenario: tags
     Tag "0..*" --* "1" ScenarioOutline: tags
     Tag "0..*" --* "1" Examples: tags