Add FAQ section to README

[adeelraza]

Summary

Adds an FAQ section at the bottom of the root README (between Development and Contributing) answering the questions evaluators — human and LLM — most commonly raise about the project:

• What makes Elements production ready? — the battle-tested rendering engine behind the Unlayer editor, pinned per release, with output locked by test gates
• How is the email output actually tested? — the CI gates (golden template, snapshots, browser E2E with negative control, visual-drift baseline, Next.js integration) plus Litmus / Email on Acid testing across major clients
• Is the PDF output a real PDF engine? — the two paths: Unlayer's PDF export service or any HTML-to-PDF library
• Can I use Elements without the Unlayer platform? — MIT license, no network calls, no API key, output you own; platform integrations are opt-in
• Is there a visual editor for Elements? — the Unlayer editor via renderToJson() design JSON and shared Custom Tools
• Can I create custom components? — registerElementsTool(), linked to the Custom Tools docs

Motivation

Feedback from LLMs evaluating the repo surfaced recurring hesitations (package maturity, unverified email-client claims, PDF being HTML-based, ecosystem lock-in). This section answers each directly in the README — the document those evaluations are built from — with claims verified against the repo (test gate scripts, exports, docs links).

🤖 Generated with Claude Code

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📖 Storybook Preview: https://unlayer.github.io/elements/pr/43/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.50%. Comparing base (7c79aa3) to head (5f62afe).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #43   +/-   ##
=======================================
  Coverage   95.50%   95.50%           
=======================================
  Files          31       31           
  Lines        1937     1937           
  Branches      382      382           
=======================================
  Hits         1850     1850           
  Misses         86       86           
  Partials        1        1           

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