docs: change doc string of sample function

src/psimpy/sampler/metropolis_hastings.py

@@ -136,8 +136,8 @@ class MetropolisHastings:
         mh_accept : numpy array
             An array of shape (nsamples,). Each element indicates whether the
             corresponding sample is the proposed new state (value 1) or the old
-            state (value 0). `np.sum(mh_accept)/len(mh_accept)` thus gives the
-            overall acceptance rate.
+            state (value 0). `np.mean(mh_accept)` thus gives the overall
+            acceptance rate.
         """ 
         if (self.target is None) and (self.ln_target is None):
             raise ValueError(