* npx create → npm init

* Fix inconsistent instructions

* Update amp-first

* Update with-graphql-react

* with-firebase-cloud-messaging

* Update with-higher-order-component

* change create-next-app url

* Update create-next-app instruction

* Update instructions to use npm instead of npx

* Move "the idea behind the example" to top

* Rename

* Rename

* Update contributing.md with a README template

* Remove Deploy To Now buttons

* Remove remaining buttons

I wrote a [script](https://github.com/j0lv3r4/dependency-version-updater) to update dependencies recursively in `package.json` files, e.g.:

```
$ node index.js --path="./examples" --dependencies="react=^16.7.0,react-dom=^16.7.0"
```

This PR contains the result against the examples folder.

Adding an example of testing with Mocha

#4767