Add docs for lh_sampling_dtype

nifty6/minimization/metric_gaussian_kl.py

@@ -115,11 +115,16 @@ class MetricGaussianKL(Energy):
         If MPI is enabled, samples will be distributed as evenly as possible
         across MPI.COMM_WORLD. If `mirror_samples` is set, then a sample and
         its mirror image will always reside on the same task.
+    lh_sampling_dtype : type
+        Determines which dtype in data space shall be used for drawing samples
+        from the metric. If the inference is based on complex data,
+        lh_sampling_dtype shall be set to complex accordingly. The reason for
+        the presence of this parameter is that metric of the likelihood energy
+        is just an `Operator` which does not know anything about the dtype of
+        the fields on which it acts. Default is float64.
     _samples : None
         Only a parameter for internal uses. Typically not to be set by users.
 
-FIXME: lh_sampling_dtype not documented!
-
     Note
     ----
     The two lists `constants` and `point_estimates` are independent from each