docs: update README to include note on decoupled model responses

[mattwittwer]

What does the PR do?

Adding a note to clarify the collection of results from decoupled model requests. This has caused some confusion since this is different from response collection using '.get()' from fixed length responses.

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• Changes are described in the pull request.
• Related issues are referenced.
• Populated github labels field
• Added test plan and verified test passes.
• Verified that the PR passes existing CI.
• Verified copyright is correct on all changed files.
• Added succinct git squash message before merging ref.
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• build
• ci
• docs
• feat
• fix
• perf
• refactor
• revert
• style
• test

Related PRs:

Where should the reviewer start?

Review the added note and the links to decoupled models and example code.

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[oandreeva-nv]

lgtm