Fix typo in dockerfile and improved Readme

[jaegeral]

This PR updates the README.md to:

• Improve clarity on what capa is.
• Add a "Workflow" section detailing how the worker processes tasks and handles input/output within the OpenRelik ecosystem.
• Refine the "Testing" section for better readability.

Additionally, adjustments were made to the Dockerfile (details should be in the commit history or file diff).

[codecov]

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All modified and coverable lines are covered by tests ✅

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