added input transform to docstring

src/bayesvalidrox/surrogate_models/gaussian_process_sklearn.py

@@ -101,6 +101,8 @@ class GPESkl(MetaModel):
             >>> MetaModelOpts.n_pca_components = 12 # Option B
     verbose : bool
         Prints summary of the regression results. Default is `False`.
+    input_transform: str
+        Type of transformation to apply to the inputs. Default is user.
     """
 
     def __init__(self, input_obj, meta_model_type='GPE', gpe_reg_method='LBFGS', n_restarts=10,