docs(claude): add basic CLAUDE.md

Author: themightychris

.claude/CLAUDE.md

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+# GTFS-RT Sandbox Project
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+This repository contains a sandbox project for introducing transit data analysts to working with tools like dbt and exploring the [TIDES](https://tides-transit.org/) data standard.
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+A key goal is to keep everything simple, fool-proof, and self-explanatory so that code is easy to read and the workflow is easy to reason about. This is an educational repository that should teach the employed concepts both through code and documentation.