✨ Help Documentation

# Overview
Help documentation will be needed for the CodeEdit application and Extension API. ~~@austincondiff and I discussed using the DocC documentation compiler, which converts Markdown-based text into documentation for Swift projects. This is the same documentation framework used by Xcode.~~

DocC is being used for internal documentation. GitBook is being used for the extension API documentation and is WIP. Please see the [Extension API Repository](https://github.com/CodeEditApp/documentation).