Composer error when using Sendgrid without composer

[warpdesign]

Issue Summary

A summary of the issue and the environment in which it occurs. If suitable, include the steps required to reproduce the bug. Please feel free to include screenshots, screencasts, or code examples.

Steps to Reproduce

1. Download and unpack sendgrid-php latest release from the GitHub downloads
2. Create a file with the sample code found here
3. Correctly modify the link to point to sendgrid-php.php from the downloaded release

Code Snippet

    require 'sendgrid-php/sendgrid-php.php';

    $email = new \SendGrid\Mail\Mail(); 
    $email->setFrom("test@example.com", "Example User");
    $email->setSubject("Sending with SendGrid is Fun");
    $email->addTo("test@example.com", "Example, User");
    $email->addContent("text/plain", "and easy to do anywhere, even with PHP");
    $email->addContent(
        "text/html", "<strong>and easy to do anywhere, even with PHP</strong>"
    );
    $sendgrid = new \SendGrid('APIKEY');
    try {
        $response = $sendgrid->send($email);
        print $response->statusCode() . "\n";
        print_r($response->headers());
        print $response->body() . "\n";
        print "mail sent";
    } catch (Exception $e) {
        echo 'Caught exception: '. $e->getMessage() ."\n";
    }   

Exception/Log

Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.3.0".

Technical details:

• sendgrid-php version: 8.1.2
• php version: 5.6

[warpdesign]

After reading the readme, it seems PHP 7.3 is required. I am closing this issue but the official sendgrid-php guide isn't up to date and mentions PHP 5.6 is supported: it should be updated, or at least mentions only sendgrid 7.x supports PHP 5.6.