docs: improve the example code for autoLogin (#4019)

Author: kobenguyent

docs/plugins.md

@@ -65,12 +65,14 @@ If a session expires automatically logs in again.
 ```js
 // inside a test file
 // use login to inject auto-login function
+Feature('Login');
+
 Before(({ login }) => {
    login('user'); // login using user session
 });
 
-// Alternatively log in for one scenario
-Scenario('log me in', ( {I, login} ) => {
+// Alternatively log in for one scenario.
+Scenario('log me in', ( { I, login } ) => {
    login('admin');
    I.see('I am logged in');
 });

lib/plugin/autoLogin.js

@@ -38,12 +38,14 @@ const defaultConfig = {
  * ```js
  * // inside a test file
  * // use login to inject auto-login function
+ * Feature('Login');
+ *
  * Before(({ login }) => {
  *    login('user'); // login using user session
  * });
  *
- * // Alternatively log in for one scenario
- * Scenario('log me in', ( {I, login} ) => {
+ * // Alternatively log in for one scenario.
+ * Scenario('log me in', ( { I, login } ) => {
  *    login('admin');
  *    I.see('I am logged in');
  * });