message: docs: add ngUpgrade maintenance timeline
  Add details about the maintenance timeline for ngUpgrade, reflecting
  the deprecation of AngularJS.
  PR Close
diff: @@ -193,6 +193,12 @@ seamlessly. That means you don't have to do the upgrade work all at once,
  since there's a natural coexistence between the two frameworks during the
  transition period.
  +<div class="alert is-helpful">
  +With the <a href="https://blog.angular.io/finding-a-path-forward-with-angularjs-7e186fdd4429">
  +deprecation of AngularJS</a>, ngUpgrade is now in a feature complete state. We will continue
  +publishing security and bug fixes until December 31st, 2022.
  +</div>
  +
  ### How ngUpgrade Works
  One of the primary tools provided by ngUpgrade is called the `UpgradeModule`.
  