add beta tag

Author: kmcfaul

packages/react-core/src/components/Masthead/examples/Masthead.md

@@ -3,6 +3,7 @@ id: Masthead
 section: components
 cssPrefix: pf-c-masthead
 propComponents: ['Masthead', 'MastheadToggle', 'MastheadMain', 'MastheadBrand', 'MastheadContent']
+beta: true
 ---
 
 import BarsIcon from '@patternfly/react-icons/dist/js/icons/bars-icon';