[dotnet] Simplify nuget package readme code example

Author: nvborisenko

dotnet/src/webdriver/assets/README.md

@@ -6,13 +6,11 @@ Selenium is a set of different software tools each with a different approach to
 using OpenQA.Selenium.Chrome;
 using OpenQA.Selenium;
 
-var driver = new ChromeDriver();
+using var driver = new ChromeDriver();
 
 driver.Url = "https://www.google.com";
 driver.FindElement(By.Name("q")).SendKeys("webdriver" + Keys.Return);
 Console.WriteLine(driver.Title);
-
-driver.Quit();
 ```
 
 # Contributing