Update file README.md

README.md

 # puml includes
 Utility project to include some common PlantUML files, that are used in the UML diagrams of the project
+
 They have to be publicly available somewhere due that the "!include" directive of PlantUML doesn't work in Gitlab (see https://gitlab.com/gitlab-org/gitlab/-/issues/28847)
+
+The UML files of EMERALD typically include several common files to define common graphical elements (arrows, colors, names, etc.). For example:
+
+```plantuml
+
+@startuml RCM Sequence Diagram
+!include ../roles.wsd
+
+[..]
+
+@enduml
+```
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