Updatte in doc/sluggable.md

doc/sluggable.md

@@ -306,6 +306,8 @@ Yaml mapped Article: **/mapping/yaml/Entity.Article.dcm.yml**
 
 - **slugField** (optional, default="slug") - the slug field where the slug will be stored
 
+    namespace Document;
+    
     class Article
     {
         // ...