docs: clarify submissions workflow

[saurabhhhcodes]

Pull Request Description

Improves the submissions workflow guide so new contributors can understand the expected folder structure, review standards, rejection reasons, and a compact example before opening a PR.

Fixes #347

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Type of Change

• New animation / hover effect
• New component
• Documentation improvement
• Bug fix in an existing submission
• Other (describe below)

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Submission Checklist

• All changes are inside submissions/examples/your-feature-name/
• Includes demo.html - self-contained, opens in browser with no server
• Includes style.css - raw CSS for the proposed feature
• Includes README.md - what it does, how to use it, why it fits EaseMotion CSS
• No changes to core/
• No changes to components/
• One feature per PR (no bundled unrelated changes)

Note: this issue explicitly asks for documentation changes in submissions/README.md, so the demo/style/submission-folder checklist items are not applicable to this PR.

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Feature Description

What does this add?

A clearer contributor workflow for building submission folders, understanding what reviewers look for, and avoiding common rejection reasons.

How does a developer use it?

Developers read submissions/README.md before creating a new folder under submissions/examples/.

Why does it fit EaseMotion CSS?

It keeps the curated submission model easier to follow and reduces review churn for new contributors.

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Demo

• Demo added (demo.html works by opening directly in a browser)

Not applicable: documentation-only workflow guide update.

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Browser Testing

• Chrome
• Firefox
• Edge
• Safari (optional but appreciated)

Not applicable: documentation-only Markdown update.

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Validation

• submission README checks passed
• git diff --check -- submissions/README.md

Note: the local clone has a pre-existing case-collision dirty file at submissions/examples/parallax-tilt-effect/README.md; it was not staged or committed.

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Notes for Maintainer

I kept this limited to submissions/README.md because #347 specifically asks for the submissions workflow docs. No core/components files were touched.

[saurabhhhcodes]

Validation proof for review:

• submission README checks passed: new workflow, good/rejected criteria, and example sections are present; Markdown fences are balanced.
• git diff --check -- submissions/README.md passed.
• No core/ or components/ files were changed.

Note: this is documentation-only for issue #347, which explicitly asks for submissions/README.md workflow docs. The local clone has a pre-existing case-collision dirty file under submissions/examples/parallax-tilt-effect that was not staged or committed.

If this is accepted for GSSoC, please add the scoring labels such as gssoc:approved, level:intermediate, type:feature or documentation.