Documentation: use case for PDF extraction

[anyacherniss]

Look at existing users + meta agent analysis: https://linear.app/anotherai-dev/issue/AAI-99/meta-agent-usage-analysis-user-patterns-and-common-challenges-sep-19#comment-64f6d21c

[anyacherniss]

Included in #343. Ideally will update the images in the page to show PDF agent