Clarify docs about toggling opt-in status via a Settings page.

Fixes #109.

README.md

@@ -152,6 +152,8 @@ do_action( 'stellarwp/telemetry/optin', '{stellar_slug}', [ 'plugin_slug' => 'th
 ## Saving Opt-In Status on a Settings Page
 When implementing the library, settings should be available for site administrators to change their opt-in status at any time. The value passed to `set_status()` should be a boolean.
 
+When a user want's to opt in, call the `Opt_In_Subscriber::opt_in` method instead of `Status::set_status` to ensure that the site is registered with the telemetry server.
+
 ```php
 add_action( 'admin_init', 'save_opt_in_setting_field' );
 
@@ -168,11 +170,16 @@ public function save_opt_in_setting_field() {
 
 	// Get an instance of the Status class.
 	$Status = Config::get_container()->get( Status::class );
+	$opt_in = Config::get_container()->get( Opt_In_Subscriber::class );
 
 	// Get the value submitted on the settings page as a boolean.
 	$value = filter_input( INPUT_POST, 'opt-in-status', FILTER_VALIDATE_BOOL );
 
-	$Status->set_status( $value );
+	if ( $value ) {
+		$opt_in->opt_in( '{stellar_slug}' );
+	} else {
+		$Status->set_status( $value );
+	}
 }
 ```