Update README with information about how to create a key

Here's what I've done:
* Go to: /admin/config/system/keys
* Click on "Add Key".
* Fill in a "Key name" eg "Sendgrid API key".
* Set the key type to "Authentication".
* Set the key provider to "Configuration".
* Paste the API key into the "Key value" field.
* Click "Save".
* Back in the Sendgrid admin page, select the new key as the "API secret key".

Disclaimer: I haven't finished setting it up, but this seems like the right direction.

I finished setting this up last night and the steps above worked.

I'll put this together as a formal docs update.

Here are the steps I used to make it work.

Thanks for the writeup, looks pretty good.

My only bit of feedback is that Key module is optional, so the "Create a key definition using the Key module" step depends on whether that module is enabled.

Otherwise, the admin/config/services/sendgrid settings are still applicable.

See SendGridSettingsForm

    $key_exists = $this->moduleHandler->moduleExists('key');

    if ($key_exists) {
      $form['authentication']['sendgrid_integration_apikey'] = [
        '#type' => 'key_select',
        '#required' => TRUE,
        '#default_value' => $config->get('apikey'),
        '#title' => $this->t('API Secret Key'),
        '#description' => $this->t('The secret key of your key pair. These are only generated once by Sendgrid.'),
      ];
    }
    else {
      $form['authentication']['sendgrid_integration_apikey'] = [
        '#type' => 'password',
        '#required' => $requirenewkey,
        '#title' => $this->t('API Secret Key'),
        '#description' => $this->t('The secret key of your key pair. These are only generated once by Sendgrid. Your existing key is hidden. If you need to change this, provide a new key here.'),
      ];
    }

You know, I never noticed that, because I already had the Key module installed for something else X-)

How about this? I split up the installation into two pieces, depending upon whether the Key module is used.

Makes sense to me, thanks!

I'll get this merged in as soon as I can.

Done! Thanks for the help!

Automatically closed - issue fixed for 2 weeks with no activity.