flexWrap, alignContent, initialPlayground

Summary: Adds `initialPlayground` to the markdown header. Adds contents fro alignContent and flexWrap.

Reviewed By: emilsjolander

Differential Revision: D6987513

fbshipit-source-id: 41de309d427a9f42e09477170fb8512ce1e7a816

website/gatsby-node.js

@@ -25,6 +25,7 @@ exports.createPages = ({boundActionCreators, graphql}) => {
             frontmatter {
               path
               hasPlayground
+              initialPlayground
             }
             html
           }