Improve the README

Add example of the output expected ...

README.md

@@ -42,9 +42,21 @@ $ make test
 
 Usage
 -----
+```
+$ gutpa [-c|-l|-m|-p <partition>|-n <interface>] [-f <sec>]
+```
 
-gutpa [-c|-l|-m|-p <partition>|-n <interface>] -i <sec>
-
+You should see something like this:
+```
+$ gupta -c 
+{
+   "timestamp": <epoch>,
+   "metrics": [
+      {"name": "cpu user", "metric": 60.0},
+	  ...
+   ]
+}
+```
 
 Removing
 --------