Add reference to tf.Module RFC.

h/t. tensorflow/community#56

PiperOrigin-RevId: 250436499
Change-Id: I9332d90f6331756f12907566af9a9e23f86aded8

sonnet/src/base.py

@@ -297,6 +297,14 @@ class Module(six.with_metaclass(ModuleMetaclass, tf.Module)):
       >>> mod = MultiplyModule()
       >>> mod(1.)
       <tf.Tensor: ... numpy=2.0>
+
+  Sonnet modules are a layer on top of `tf.Module`, implementing automatic name
+  scoping as described in the original RFC [0]_.
+
+  References:
+    .. [0] Hennigan, Tom, et al. "RFC: Stateful Containers with tf.Module."
+       TensorFlow Community RFCs, Google / DeepMind, 17 Jan. 2019,
+       https://github.com/tensorflow/community/pull/56
   """
 
   def __init__(self, name: Optional[Text] = None):