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.
I have updated [examples/with-markdown](https://github.com/zeit/next.js/tree/canary/examples/with-markdown) in order to make it works with next 6 🎉
<details>
<summary>Error</summary>
Error: Plugin/Preset files are not allowed to export objects, only functions. In /Users/zhenyatelegin/Desktop/next.js/examples/with-markdown/node_modules/markdown-in-js/babel.js
</details>
* Examples: clarify language around Yarn create & npx
* add missing READMEs and create-next-app usage
* suggest people tag jthegedus in firebase related issues
* add yarn alt instructions
* cerebraljs example readme & fixes
* remove global npm install of create-next-app
* add npx to create-next-app command in examples
* add bash to shell snippets
* add yarn create to next-app command in examples
* fix READMEs named with lowercase
* change READMEs to use UPPERCASE
