Update deprecated-features.rst (#7716)

* Update deprecated-features.rst

* Update source/about/deprecated-features.rst

---------

Co-authored-by: Carrie Warner (Mattermost) <[email protected]>

Author: amyblais

source/about/deprecated-features.rst

@@ -6,6 +6,11 @@ This page describes features that are removed from support for Mattermost, or wi
 Removed features in upcoming versions
 -------------------------------------
 
+Mattermost Server v10.6.0
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+- Support for PostgreSQL v11 and v12 will be removed. The new minimum PostgreSQL version will be v13+. See the :ref:`minimum supported PostgreSQL version policy <install/prepare-mattermost-database:minimum supported version policy>` documentation for details.
+
 Mattermost Mobile App v2.25.0
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~