Documentation: fix "Send Multiple Emails to Multiple Recipients"?

Issue Summary

The "Send Multiple Emails to Multiple Recipients" documentation section basically uses this to demonstrate sending an email to multiple recipients:

new Mail(
    $from,
    [new To("test+test1@example.com"), new To("test+test2@example.com")],
    // ...
);

In our use case (no substitution, same body for everyone, meaning to send a separate email to each recipient individually), this lead to sending a single email with everyone in the "to" recipients list.

The right way to achieve this is to use create N Personalizations:

$email = new Mail(
    new From(self::MAIL_FROM, self::FROM_NAME),
    null,
    new Subject($subject),
    $plainTextContent,
    $htmlContent
);

// Add recipients
foreach ($emails as $emailAddress) {
    // Note: "To" constructor may throw an exception when encountering an invalid email.
    try {
        $personalization = new Personalization();
        $personalization
            ->addTo(new To($emailAddress));

        $email->addPersonalization($personalization);
    } catch (TypeException $ex) {
        continue;
    }
}

Are mails separately sent only if there is at least one substitution? Shouldn't we update the documentation to add a warning if that's the case?

Waiting for feedback before opening a PR to update the documentation!

Steps to Reproduce

Try to send n emails to n recipients
Use the example in the documentation (->addTo(new To($email)))
Notice that a single mail is sent, with n recipients instead

Technical details:

sendgrid-php version: latest
php version: php7.4

sendgrid / sendgrid-php

Documentation: fix "Send Multiple Emails to Multiple Recipients"? #1040

Issue Summary

Steps to Reproduce

Technical details: