The goal of Starter is to be a starting point for your projects and, as such, there are two types of documentation; the first type is, by default, a simple template for you to eventually update as your project progresses:
Documentation specific to the project that you build on top of Starter
The second type, which is where you should begin, aims to describe what Starter is, how to install and use it, etc.:
Documentation specific to Starter itself
Starter is developed by the folks at The Outfit.