Add a Developer "Getting started" guide

[mynameistechno]

Issue Report

Add documentation for getting started with repolinter development.

Expected Behavior

Docs that outline steps on systems dependencies, how to install repolinter locally, and how to run the tests.

[mynameistechno]

The github actions are a good place to start https://github.com/todogroup/repolinter/blob/master/.github/workflows/ci.yaml