Adds manifest.json to examples folder (#3536)

* Revert "Revert "[examples] Add manifest.json""

This reverts commit c65336e63b.

* Revert "Revert "Do not use now-examples anymore""

This reverts commit ac72e944a7.

* Update nowignore

* Fix join

* Fix JSON

* Fix header

* Replace manifest.json with @now/frameworks

* Adjust readmes

* Adjust .nowignore

* Update scully

* Fix description

* Update examples/create-react-app/src/App.js

Co-Authored-By: Shu Ding <ds303077135@gmail.com>

* Update readme

* Add websites

* Use https

* Adjust example URL

* Change order

Co-authored-by: Shu Ding <ds303077135@gmail.com>

api/_lib/examples/map-old-to-new.ts

@@ -21,6 +21,7 @@ export const mapOldToNew: { [key: string]: string[] } = {
   'nuxt-static': ['nuxtjs'],
   static: ['vanilla'],
   typescript: ['gatsby-functions'],
+  umi: ['umijs'],
   'vanilla-go': ['vanilla-functions'],
   'vanilla-json-api': ['svelte-functions'],
   'vue-ssr': ['vue'],