Add getting started content to README

[pcolange]

The current README lacks content on how to use Digest AI and what specific features it offers. This issue is a request to add that content to help bootstrap new users. Specifically:

• Add headlines about features and usage to README
• Document the feature of reading in digest reports ([Resolves] Support ingesting a digest model report/cache #3)
• Refer folks to https://www.amd.com/en/developer/resources/technical-articles/digest-ai-model-ingestion-and-analysis-tool.html (and any other related content) for in depth usage/guide.