Create a new markdown document through interactive CLI in Riff

[aManNamedJed]

We are getting a little particular about how users shape their Markdown frontmatter at the top of each document and I want to give folks the ability to create a documentation file easily through riff

---
title: Using the monorepo
date_created: '2020-04-12'
date_updated: '2020-04-12'
keywords: 'monorepo, gatsby, starter'
path: /docs/v0.1.0/monorepo
description: Getting set up with Rockin' Blocks is a breeze.
order: '2.1'
type: document
---

It would be cool to have some type of interactive CLI, but maybe in this early version folks can just give me the name of the file and I will put it in the right spot with some boilerplate in it.

There's already an example of me creating a Block already, but we would need the Subcommands issue completed before this can be completed.