meta: add release working group

Was recently chartered in as per
nodejs/Release#223

PR-URL: #167
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

Author: mhdawson

WORKING_GROUPS.md

@@ -41,6 +41,7 @@ Top Level Working Group](https://github.com/nodejs/TSC/blob/master/WORKING_GROUP
 * [Benchmarking](#benchmarking)
 * [Post-mortem](#post-mortem)
 * [Intl](#intl)
+* [Release](#release)
 
 
 ### [Website](https://github.com/nodejs/nodejs.org)
@@ -248,3 +249,17 @@ Responsibilities include:
   to be generated when needed.
 * Defining and adding common structures to the dumps generated
   in order to support tools that want to introspect those dumps.
+
+### [Release](https://github.com/nodejs/release)
+
+The Release Working Group manages the release process for Node.js.
+
+Responsibilities include:
+* Define the release process.
+* Define the content of releases.
+* Generate and create releases.
+* Test Releases.
+* Manage the Long Term Support and Current branches including
+  backporting changes to these branches.
+* Define the policy for what gets backported to release streams.
+