update changelog and docstring

CHANGELOG.md

@@ -6,6 +6,7 @@
 * Added `arviz.labels` module with classes and utilities ([1201](https://github.com/arviz-devs/arviz/pull/1201))
 * Added probability estimate within ROPE in `plot_posterior` ([1570](https://github.com/arviz-devs/arviz/pull/1570))
 * Added `rope_color` and `ref_val_color` arguments to `plot_posterior` ([1570](https://github.com/arviz-devs/arviz/pull/1570))
+* Improved retrieving or pointwise log likelihood in `from_cmdstanpy` ([1579](https://github.com/arviz-devs/arviz/pull/1579))
 
 ### Maintenance and fixes
 * Enforced using coordinate values as default labels ([1201](https://github.com/arviz-devs/arviz/pull/1201))

arviz/data/io_cmdstanpy.py

@@ -727,7 +727,11 @@ def from_cmdstanpy(
  predictions_constant_data : dict
  Constant data for predictions used in the sampling.
  log_likelihood : str, list of str, dict of {str: str}
- Pointwise log_likelihood for the data.
+ Pointwise log_likelihood for the data. If a dict, its keys should represent var_names
+ from the corresponding observed data and its values the stan variable where the
+ data is stored. By default, if a variable ``log_lik`` is present in the Stan model,
+ it will be retrieved as pointwise log likelihood values. Use ``False`` to avoid this
+ behaviour.
  index_origin : int, optional
  Starting value of integer coordinate values. Defaults to the value in rcParam
  ``data.index_origin``.