Update README

Author: leonlan

README.md

@@ -17,7 +17,26 @@ pip install psplib
 
 ## Example usage
 
-See [this](https://github.com/PyJobShop/PSPLIB/blob/main/example.ipynb) notebook for an example demonstration of PSPLIB.
+``` python
+>>> from psplib import parse
+>>> instance = parse("data/j301_1.sm", instance_format="psplib") 
+>>> instance.num_resources
+4
+
+>>> instance.resources
+[Resource(capacity=12, renewable=True), ..., Resource(capacity=12, renewable=True)]
+
+>>> instance.num_activities
+32
+
+>>> instance.activities
+[Activity(modes=[Mode(duration=0, demands=[0, 0, 0, 0])], successors=[1, 2, 3], delays=None, name=''), 
+ Activity(modes=[Mode(duration=8, demands=[4, 0, 0, 0])], successors=[5, 10, 14], delays=None, name=''),
+ ...,
+ Activity(modes=[Mode(duration=0, demands=[0, 0, 0, 0])], successors=[], delays=None, name='')]
+```
+
+See [this](https://github.com/PyJobShop/PSPLIB/blob/main/example.ipynb) notebook for a slightly longer example demonstration of PSPLIB.
 
 ## Instance formats