Update README.md

Author: olexale

README.md

@@ -55,6 +55,9 @@ Feature file sample:
 
 Feature: Counter
 
+  Background:
+    Given the answer is {42}
+
   Scenario: Initial counter value is 0
     Given the app is running
     Then I see {0} text
@@ -65,6 +68,8 @@ Feature: Counter
     Then I see {1} text
 ```
 
+`Backround` keyword is optional. A Background allows you to add some context to the scenarios that follow it. It can contain one or more Given steps, which are run before each scenario.
+
 Each feature file must have one or more `Feature:`s. Features become test groups in Flutter tests.
 
 Each feature group must have one or more `Scenario:`s (or `Example:`s). Scenario become widget tests.