write best-practices guide for safe, efficient, and effective usage

[clockelliptic]

To Do: write best-practices guide for safe, efficient, and effective usage

Why:

• so that it's clear how to make safe, efficient, and effective use of device storage
• as that usage results in the most performant and effective outcomes
• because this this library is flexible and convenient enough that it can be accidentally misused

Acceptance Criteria:

• adds README documentation with best practices and scenarios
• includes guidance on how to segment cache keys so that automatic pruning is effective on a per-app-page basis
• includes guidance on when not to use this library
• includes guidance on safe or effective alternatives for cases when this library is not a good fit
• includes clear guidance on when to use this in lieu of service workers or a PWA
• includes clear guidance on the vulnerabilities of IndexedDB caching compared to browser cache API