Rename ‘up’ to ‘cloudup’ and update install instructions

The npm package name `up` has been assumed by [apex/up](https://github.com/apex/up), thus cloudup-cli can no longer be installed with `npm install -g up`. I recommend cloudup-cli be renamed to `cloudup` so it can be installed with `npm install -g cloudup` and can be installed in parallel with the new `up`.

In the meantime, cloudup-cli can be installed by referencing the github repo directly, like this:

npm install -g Automattic/cloudup-cli

Start by locating the package metadata and installation instructions that still identify the executable as `up`. Update the package and documented commands so the CLI installs as `cloudup`, then verify the documented npm installation path and the existing GitHub installation workaround.

Written by the indexing model from the issue text.