Change pip install to install extra requires

Author: JoaoFelipe

README.md

@@ -44,10 +44,9 @@ you should run the tests:
 
 ```bash
 # First install the python package. This will also build the JS packages.
-pip install -e .
+pip install -e ".[test, examples]".
 
 # Run the python tests. This should not give you a few sucessful example tests
-# You may need to install nbval first: pip install nbval
 py.test
 
 # Run the JS tests. This should again, only give TODO errors (Expected 'Value' to equal 'Expected value'):