message: Adding documentation on BIS No New Model Properties Rule
  Adding to schema validation documentation:
  Subclasses of **bis:Model** cannot have additional properties defined outside of **BisCore**.
diff: @@ -52,6 +52,7 @@ The rules are broken into the different parts of the Schema they are validated a
  - **bis:DocumentListModel**
  - **bis:LinkModel**
  - Property overrides cannot change the persistence unit.
  +- Subclasses of **bis:Model** cannot have additional properties defined outside of **BisCore**.
  ### Relationship Classes
  