New starter kit: contributor guide

Purpose

To create an outline for a Contributors Guide that SLIM community folks can agree upon as having value
To flush out sections such as Prerequisites, Development Process, Issue Ticket Contributions
Currently this PR does not contain guidance on code contributions, documentation, questions, etc. Those can be submitted in an add-on PR once we agree to the outline proposed here (or altered)
Proposed Changes
[ADD] New contributions guide section within starter kit
[CHANGE] Updated Markmap to point to new starter kits
Testing
Demo available at: https://github.com/riverma/terraformly/blob/main/CONTRIBUTING.md
Tested locally using RETYPE on Mac OSX Big Sur & Safari 15.3 (see example below)