Add question to change output directory

[bencodezen]

Problem

Currently the tool is created to take an optional folderDirectoryName after the command:

yarn create vuepress-site [optionalDirectoryName]

If provided, it will attempt to create a new folder called [optionalDirectoryName] and then drop all of the template files in there.

This is not intuitive and many will miss this.

Proposal

1. Remove the optional argument from the command entirely
2. CLI prompt should inform user what folder is about to be created. It defaults to docs
3. User can specify a different directory that will contain all of the template files