Generate nicer READMEs inside new projects/apps/views/packages.

[threepointone]

These are the READMEs we currently generate

• For a new project: https://github.com/jpmorganchase/modular/blob/master/packages/create-modular-react-app/template/README.md
• In a new app: https://github.com/jpmorganchase/modular/blob/master/packages/modular-scripts/cra-template-modular-typescript/template/README.md
• In a new view: https://github.com/jpmorganchase/modular/blob/master/packages/modular-scripts/types/view/README.md
• In a new package: https://github.com/jpmorganchase/modular/blob/master/packages/modular-scripts/types/package/README.md

They're all embarrassingly light, we should rewrite all of them. The one for the app isn't even correct, it's copied from create-react-app.

Related issue: #58

[cristiano-belloni]

#2253