message: IMPROVE message when buildStorybookDir is empty
diff: @@ -119,7 +119,9 @@ async function prepareAppOrBuild({
  if (buildScriptName) {
  throw new Error(`Storybook was not build succesfully, there are likely errors above`);
  } else {
  - throw new Error(`The folder you specified (${buildDirName}) doesn't exist`);
  + throw new Error(dedent`
  + It looks like your storybook build (to directory: ${buildDirName}) failed, as that directory is empty. Perhaps something failed above?
  + `);
  }
  }
  