Throw when using Stage presets (#8293)

* inline stage presets into standalone, throw error with using Stage presets

scripts/generators/readmes.js

@@ -66,6 +66,7 @@ yarn add ${name} --dev
 
 packages
   .filter(x => x !== "README.md") // ignore root readme
+  .filter(x => x.indexOf("babel-preset-stage-") === -1) // ignore stages
   .forEach(id => {
     const { name, description } = getPackageJson(id);
     const readmePath = join(packageDir, id, "README.md");