Document how to run mongo in local development

[MrGreenTea]

• cp .env.example .env
• podman volume create yv-homepage-payload-mongo-data
• podman run -d --publish 27017:27017 -v yv-homepage-payload-mongo-data:/data/db docker.io/library/mongo

The DATABASE_URI in .env.example should probably be mongodb://127.0.0.1/website