Document Phabricator as no longer actively maintained

Summary: Ref T13654.

Test Plan: Read document.

Maniphest Tasks: T13654

Differential Revision: https://secure.phabricator.com/D21664

README.md

@@ -1,30 +1,6 @@
-**Phabricator** is a collection of web applications which help software companies build better software.
+Effective June 1, 2021: Phabricator is no longer actively maintained.
 
-Phabricator includes applications for:
-
-  - reviewing and auditing source code;
-  - hosting and browsing repositories;
-  - tracking bugs;
-  - managing projects;
-  - conversing with team members;
-  - assembling a party to venture forth;
-  - writing stuff down and reading it later;
-  - hiding stuff from coworkers; and
-  - also some other things.
-
-You can learn more about the project (and find links to documentation and resources) at [Phabricator.org](http://phabricator.org)
-
-Phabricator is developed and maintained by [Phacility](http://phacility.com).
-
-----------
-
-**SUPPORT RESOURCES**
-
-For resources on filing bugs, requesting features, reporting security issues, and getting other kinds of support, see [Support Resources](https://secure.phabricator.com/book/phabricator/article/support/).
-
-**NO PULL REQUESTS!**
-
-We do not accept pull requests through GitHub. If you would like to contribute code, please read our [Contributor's Guide](https://secure.phabricator.com/book/phabcontrib/article/contributing_code/).
+**Phabricator** is a collection of web applications for software development.
 
 **LICENSE**