docs: explain how to provide input documents to the agent (#250)

[valter-silva-au]

Summary

Closes #250.

The writing-inputs guides explain what a Vision Document and Technical Environment Document are and how they feed each AI-DLC stage, but never tell the user the mechanical step of how to hand a document to the agent or where to place it. As reported in #250, a user who asked "where do I put a vision document?" got a confused, non-definitive answer.

This adds the missing instruction, matching the fix @leandrodamascena outlined in the issue thread.

Changes

Add a short "How to Provide … to the Agent" section near the top of both:

• docs/writing-inputs/vision-document-guide.md
• docs/writing-inputs/inputs-quickstart.md

The section states the intended flow: place the document anywhere in your project and reference it in your initial request (e.g. read ./vision.md and start the AI-DLC workflow), or paste its contents into chat — no enforced folder convention.

Docs-only and additive; no rules, code, or behavioral change. (The issue also floated a tweak to requirements-analysis.md, but its Step 4 already instructs the agent to use "existing requirements documents (search workspace if mentioned)" and "pasted content or file references", so the genuine remaining gap was the user-facing docs.)

User experience

• Before: The guides describe the documents thoroughly but never say where to put one or how the agent picks it up; users are left guessing and the agent gives non-definitive answers.
• After: Both entry-point docs state up front how to provide an input document — reference it by path in the initial request, or paste it — and that no specific folder is required.

Checklist

• I have reviewed the contributing guidelines
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Test Plan

• markdownlint-cli2 (the repo's CI lint, .markdownlint-cli2.yaml) passes on both files with 0 errors.
• The CI multiple-choice-separator check (issue [Bug]: Question-format template renders as a single paragraph in strict CommonMark renderers (IntelliJ/PyCharm preview, etc.) #246) passes — no A) -style consecutive lines introduced.
• Render both files and confirm the new section appears near the top and reads correctly.

Acknowledgment

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of the project license.

[valter-silva-au]

Heads-up on CI: the Security Scanners workflow (gitleaks/grype) shows red, but it's failing on main independently of this PR — the scheduled runs on main are red too, and this change is docs-only (+22 lines of markdown, no secrets or dependency changes). The separate gitleaks/grype checks that scan this PR's content pass, as do Markdown Lint, the contributor-statement check, and PR-title validation. Happy to rebase if you'd like once that workflow is addressed on main.