docs: explain browser impersonation helpers

[w3lld1]

Summary

• Document when to use impersonate_validate instead of generic_validate
• Explain warmup_url, impersonate, and show_url
• Add a usage example and note when impersonate_request is useful for multi-step flows

Validation

• git diff --check
• Documentation assertions against the live helper signatures
• Python syntax validation for the new example

The full test and lint suites were not run locally because the dependency environment could not be installed within the available disk quota; I deferred them to CI because this change only updates documentation.

Fixes #464

[brunolm]

1. Document allow_redirects (default False) and the httpx name difference (follow_redirects vs allow_redirects).

- `allow_redirects` defaults to `False` (curl_cffi). This is the opposite of httpx’s `follow_redirects=True` used with `generic_validate`; pass `allow_redirects=True` when the profile URL redirects. Extra kwargs are forwarded to `impersonate_request`.

2. Example taken check is too weak (user in response.text); align with CRITICAL rule 1.

    def process(response):
        if response.status_code == 404 and "User does not exist" in response.text:
            return Result.available()
        if response.status_code == 200 and f'profile/{user}' in response.text:
            # Prefer a unique body marker (title, canonical, embedded user id) —
            # not a bare `user in response.text` check (boilerplate false positives).
            return Result.taken()
        return Result.error(f"Unexpected response status: {response.status_code}")

[w3lld1]

Thanks — addressed both documentation points in 542e350:

• documented that allow_redirects defaults to False, contrasted it with httpx's follow_redirects, and noted that additional keyword arguments are forwarded;
• strengthened the example so both available and taken results require explicit, state-specific body markers.

Fresh validation: focused documentation assertions and git diff HEAD^ --check.

[kaifcodec]

LGTM.
Thank you @w3lld1 for the contribution.
Feel free to explore the project and contribute further.