Update entities.md

Author: themiszamani

docs/pid_kb_theory/entities.md

@@ -17,7 +17,10 @@ There are two additional dimensions to the classification that are not currently
 
 The KB consists of multiple entities, each playing a specific role in the Persistent Identifier (PID) ecosystem.
 
-
+import entities from '/img/pid_kb/db_kb.png';
+ 
+ <img src={entities} alt="Entities in the PID Knowledge Base " style={{width: 600}} />
+ 
 
 ## Core Entities