Encourage local installation of @ionic/cli package

## Problem Statement
Currently, the [installation docs](https://ionicframework.com/docs/cli#installation) recommends global installation of the cli. This can be annoying when you have to maintain different projects with different ionic framework versions (for example ionic framework 3 and 4) because one cli does not work with the other version of the framework.

## Suggested changes
It's been a while since npm has introduced npx. I don't see any good reason to install cli globally anymore.
So I would like to propose a change in the documentation to recommend the local installation of cli.

But because of how cli works currently, it requires `native-run` to be installed globally. So if it's possible, I would also like to propose to change this behavior of cli to work with `native-run` installed locally.

Another advantage of installing cli locally is making the initial setup of the project in a new machine much easier. With this, `npm install` should take care of everything ideally.