docs: update Circom optimization guidance

[strongkeep-debug]

This updates the verifier usage guide's Circom optimization note to match the current compiler behavior:

Area	Change	Evidence
docs/zk-email-verifier/usage-guide.md	Clarifies that --O1 is the default since Circom 2.2.0, while --O2 was the pre-2.2.0 default and should be reserved for final optimization passes.	Circom constraint simplification docs linked inline.
Beginner guidance	Keeps the --O0 recommendation for easier constraint inspection while removing the incorrect claim that --O2 is the default.	Local docs build completed.

Validation run locally:

POSTHOG_API_KEY=phc_dummy_for_local_build npx --yes yarn@1.22.22 build
[SUCCESS] Generated static files in build.

git diff --check
clean

Fixes #32.

Summary by CodeRabbit

• Documentation
  • Updated compilation guide with clearer guidance on Circom optimization flags, including recommended --O0 setting for beginners, version-specific defaults for Circom 2.2.0+, and refined recommendations for performance optimization.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: f983a21d-c936-4a91-890d-f97e37420fd6

📥 Commits

Reviewing files that changed from the base of the PR and between dbd0360 and 35f6e50.

📒 Files selected for processing (1)

• docs/zk-email-verifier/usage-guide.md

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📝 Walkthrough

Walkthrough

This pull request updates the Circom compilation documentation in the zk-email-verifier usage guide to correct outdated information about default optimization flags and clarify include directory behavior. The note now recommends --O0 for beginners, documents --O1 as the current default in Circom 2.2.0+, and advises caution with --O2.

Changes

Circom Compilation Documentation

Layer / File(s)	Summary
Compilation flag guidance clarification docs/zk-email-verifier/usage-guide.md	Step 3's compilation note is expanded to explain -l for include path resolution, recommends --O0 for beginners, documents the --O1 default in Circom 2.2.0+, discourages --O2 without sufficient constraint familiarity, and adds a reference link to Circom's simplification documentation.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

A note for the wise, by circuits besieged,
Now clarifies flags that beginners are eased.
-l for includes, and -O0 to start,
Before ventures bold into optimization's art! 🐰✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The pull request title accurately and concisely summarizes the main change: updating Circom optimization guidance in the documentation.
Linked Issues check	✅ Passed	The pull request fully addresses all coding objectives from issue #32: replacing incorrect --O2 default claim with correct --O1 default information, noting pre-2.2.0 behavior, adjusting beginner guidance, and adding reference documentation.
Out of Scope Changes check	✅ Passed	All changes in the pull request are directly scoped to fixing the documentation issue in the specified file section; no out-of-scope modifications are present.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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