uml/state-machine-diagram.md

-**Sources:** http://www.omg.org/spec/UML/2.5 (Starting at PDF page 345)
+**Sources:**
+- http://www.omg.org/spec/UML/2.5 (Starting at PDF page 345)
+- trigger specification (including when/after/at): Starting at PDF page 333
 
 # Usage Scenarios
 The **state machine diagram** is used to illustrate the life-cycle of single objects and the behavior of operations within a software system