Edit and make README more modular

@gvwilson I've split the existing `README.md` into 3 files to simplify the end user experience when setting up a new workshop and its repos. 

This PR focuses on walking the user through dependencies, install process, customizing the repos, FAQ, getting help, and contact info. 

I split off the customization process and rationale into a separate but linked markdown file `CUSTOMIZATION.md`. The FAQ is also a standalone document linked from the README since it is likely the FAQ will be edited with greatest frequency and will make it easier for maintainers to quickly review without risk of changing the installation instructions.