Add a note in the README indicating that this repository is no longer updated.
Add a note in the README indicating that this repository is no longer updated.

Summary: Add a note in the README indicating that this repository is no longer updated.

Test Plan: No code changes.

Reviewers: nate

Reviewed By: nate

Subscribers: changesbot, anupc, kylec

Differential Revision: https://tails.corp.dropbox.com/D195591

dropbox/changes-client,dropbox/changes-client