Added release notes

Author: lucianopaz

RELEASE-NOTES.md

@@ -28,6 +28,8 @@
 - Fixed a defect in `OrderedLogistic.__init__` that unnecessarily increased the dimensionality of the underlying `p`. Related to issue issue [#3535](https://github.com/pymc-devs/pymc3/issues/3535) but was not the true cause of it.
 - Wrapped `DensityDist.rand` with `generate_samples` to make it aware of the distribution's shape. Added control flow attributes to still be able to behave as in earlier versions, and to control how to interpret the `size` parameter in the `random` callable signature. Fixes [3553](https://github.com/pymc-devs/pymc3/issues/3553)
 - Added `theano.gof.graph.Constant` to type checks done in `_draw_value` (fixes issue [3595](https://github.com/pymc-devs/pymc3/issues/3595))
+- Refactored `pymc3.model.get_named_nodes_and_relations` to use the ancestors and descendents, in a way that is consistent with `theano`'s naming convention.
+- Changed the way in which `pymc3.model.get_named_nodes_and_relations` computes nodes without ancestors to make it robust to changes in var_name orderings (issue [#3643](https://github.com/pymc-devs/pymc3/issues/3643))
 
 
 ## PyMC3 3.7 (May 29 2019)