Update README.rst

Adding defined arguments; in particular dt was undefined in the example

Author: jasonmhead

README.rst

@@ -150,7 +150,7 @@ Initialize the filter's matrices.
     my_filter.H = np.array([[1.,0.]])    # Measurement function
     my_filter.P *= 1000.                 # covariance matrix
     my_filter.R = 5                      # state uncertainty
-    my_filter.Q = Q_discrete_white_noise(2, dt, .1) # process uncertainty
+    my_filter.Q = Q_discrete_white_noise(dim=2, dt=0.1, var=0.1) # process uncertainty
 
 
 Finally, run the filter.