update env-vars example

Author: raphamorim

docs/docs/config/env-vars.md

@@ -3,8 +3,10 @@ title: 'env-vars'
 language: 'en'
 ---
 
-Sets environment variables
+Sets environment variables.
+
+Example:
 
 ```toml
-env-vars = []
+env-vars = ["FIRST_VARIABLE_NAME=123", "SECOND_VARIABLE_NAME=456"]
 ```