mattermost: update release notes

nixos/doc/manual/from_md/release-notes/rl-2205.section.xml

@@ -30,6 +30,14 @@
           PHP 8.1 is now available
         </para>
       </listitem>
+      <listitem>
+        <para>
+          Mattermost has been updated to version 6.2. Migrations may
+          take a while, see the
+          <link xlink:href="https://docs.mattermost.com/install/self-managed-changelog.html#release-v6.2-feature-release">upgrade
+          notes</link>.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
   <section xml:id="sec-release-22.05-new-services">

nixos/doc/manual/release-notes/rl-2205.section.md

@@ -13,6 +13,9 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - PHP 8.1 is now available
 
+- Mattermost has been updated to version 6.2. Migrations may take a while,
+  see the [upgrade notes](https://docs.mattermost.com/install/self-managed-changelog.html#release-v6.2-feature-release).
+
 ## New Services {#sec-release-22.05-new-services}
 
 - [aesmd](https://github.com/intel/linux-sgx#install-the-intelr-sgx-psw), the Intel SGX Architectural Enclave Service Manager. Available as [services.aesmd](#opt-services.aesmd.enable).