Add directions how to setup for GitHub secrets

[danactive]

There are two sets of secrets that are stored in each GitHub repo (future might be shared across the robotsandpencils organization): mobile or web

The secret names are

• OP_DEVICE_ID
• OP_SIGN_IN_ADDRESS
• OP_EMAIL_ADDRESS
• OP_SECRET_KEY
• OP_MASTER_PASSWORD

Some of these secret values are created by 1Password admins and others are GitHub org admins

[danactive]

(reminder this repo is public open source)