Include links to new announce@ list (tensorflow#17606)

* Add ewilderj as CoC contact

* Add named contacts to code of conduct

* Update language to match multiple stewards

* Include links to new announce@ list.

README.md

@@ -22,6 +22,10 @@ organization for the purposes of conducting machine learning and deep neural
 networks research.  The system is general enough to be applicable in a wide
 variety of other domains, as well.
 
+Keep up to date with release announcements and security updates by
+subscribing to
+[[email protected]](https://groups.google.com/a/tensorflow.org/forum/#!forum/announce).
+
 ## Installation
 *See [Installing TensorFlow](https://www.tensorflow.org/get_started/os_setup.html) for instructions on how to install our release binaries or how to build from source.*
 

tensorflow/docs_src/community/welcome.md

@@ -51,6 +51,8 @@ Europe:
 TensorFlow provides multiple communication paths.  To pick the right path,
 please read the following list carefully:
 
+  * For new release announcements and security updates, subscribe to
+    [[email protected]](https://groups.google.com/a/tensorflow.org/forum/#!forum/announce).
   * To ask or answer technical questions about TensorFlow, use
     [Stack Overflow](https://stackoverflow.com/questions/tagged/tensorflow).
     For example, ask or search Stack Overflow about a particular error message