Add twilio testing instructions

Wrote these out for front/!698 but they might be useful for others.

Testing twilio

To test the phone verification step in the token onboarding process locally, you need to make some backend changes.

• in settings.php,

$CONFIG->set('twilio', [
  'account_sid' => '',//get this from Mark
  'auth_token' => '',//get this from Mark
  'from' => '+15005550006' // use this exact number
]);

• in Core/Rewards/Join.php, go to the verify() function
  • directly after this line (around 116): $code = $this->twofactor->getCode($secret);, add error_log($code)
  • comment this line (around 120): throw new \Exception('voip phones not allowed');
  • now when you enter almost any phone number in token onboarding, the corresponding verification code will appear in your php logs. Use it to complete the phone verification step. Note: the handful of phone numbers that won't work are the magic 'To' numbers listed in Twilio's test credential docs.