Add conclusion about required field documentation into design patterns doc. https://github.com/phetsims/phet-info/issues/116#issuecomment-549535230
Add conclusion about required field documentation into design patterns doc. https://github.com/phetsims/phet-info/issues/116#issuecomment-549535230

phetsims/phet-info,phetsims/phet-info,phetsims/phet-info,phetsims/phet-info