message: build(aio): process marketing docs that have .md extension
  See
diff: @@ -102,7 +102,7 @@ module.exports =
  },
  {
  basePath: CONTENTS_PATH + '/marketing',
  - include: CONTENTS_PATH + '/marketing/**/*.html',
  + include: CONTENTS_PATH + '/marketing/**/*.{html,md}',
  fileReader: 'contentFileReader'
  },
  {
  