Merge pull request #46 from joseluis/patch-2

replace deprecated getUsage() method
diff --git a/README.md b/README.md
index 764e008..9e3b3ca 100644
--- a/README.md
+++ b/README.md
@@ -363,10 +363,10 @@
     });
 ```
 
-To display the help, use the [getUsage()][getUsage] method:
+To display the help, use the [usage][usage] getter:
 
 ```dart
-print(parser.getUsage());
+print(parser.usage);
 ```
 
 The resulting string looks something like this: