add glm reference to Bambi

Author: farhanreynaldo

docs/source/api/glm.rst

@@ -4,5 +4,7 @@ Generalized Linear Models
 
 .. currentmodule:: pymc3.glm.linear
 
-.. automodule:: pymc3.glm.linear
-   :members:
+Generalized Linear Models are delegated to the
+`Bambi <https://bambinos.github.io/bambi>`_.
+library, a high-level Bayesian model-building
+interface built on top of the PyMC3.