docs: document webview sizing styles

[Rajesh270712]

Summary

• Document the CSS sizing requirements for <webview> so full-window/parent-filling use cases have a concrete example.
• Add the document contributor entry required by the docs contribution checklist.

Linked issue / bounty

• Fixes The webview tag is not sized properly #4189
• IssueHunt: https://oss.issuehunt.io/r/nwjs/nw.js/issues/4189

Problem

The issue thread shows that <webview> sizing can look broken unless the embedder page gives the element and its parent explicit sizing and a flex-compatible display. The workaround is discussed in the issue, but the reference page did not mention it.

Fix

This PR adds a docs-only note to docs/References/webview Tag.md explaining the layout requirement and includes a minimal full-window example using display: inline-flex, width: 100%, and height: 100%.

Validation

• git diff --check origin/main...HEAD
• python3 -m venv .venv && .venv/bin/python -m pip install -r requirements.txt && .venv/bin/mkdocs build
• Generated HTML/source content check for predictable sizing, full-window, inline-flex, width: 100%, and height: 100%
• GitHub issue rechecked open; no open same-surface PRs found

Risk / limitations

• Docs-only change; no NW.js runtime behavior is changed or claimed.
• The example is intentionally minimal and may need wording/placement tweaks if maintainers prefer a different style.