Added notes about running tests with Selenium Server 3.0 [skip ci]

Author: ElisDN

README.md

@@ -143,7 +143,23 @@ To execute acceptance tests do the following:
 
     ```
     java -jar ~/selenium-server-standalone-x.xx.x.jar
+    ```
+
+    In case of using Selenium Server 3.0 with Firefox browser since v48 or Google Chrome since v53 you must download [GeckoDriver](https://github.com/mozilla/geckodriver/releases) or [ChromeDriver](https://sites.google.com/a/chromium.org/chromedriver/downloads) and launch Selenium with it:
+
+    ```
+    # for Firefox
+    java -jar -Dwebdriver.gecko.driver=~/geckodriver ~/selenium-server-standalone-3.xx.x.jar
+    
+    # for Google Chrome
+    java -jar -Dwebdriver.chrome.driver=~/chromedriver ~/selenium-server-standalone-3.xx.x.jar
     ``` 
+    
+    As an alternative way you can use already configured Docker container with older versions of Selenium and Firefox:
+    
+    ```
+    docker run --net=host selenium/standalone-firefox:2.53.0
+    ```
 
 5. (Optional) Create `yii2_basic_tests` database and update it by applying migrations if you have them.