nixos/pantheon: mention latest appcenter changes in manual

Author: bobby285271

nixos/modules/services/x11/desktop-managers/pantheon.xml

@@ -105,7 +105,7 @@ switchboard-with-plugs.override {
     </term>
     <listitem>
      <para>
-      AppCenter has been available since 20.03, but it is of little use. This is because there is no functioning PackageKit backend for Nix 2.0. Starting from 21.11, the Flatpak backend should work so you can install some Flatpak applications using it. See this <link xlink:href="https://github.com/NixOS/nixpkgs/issues/70214">issue</link>.
+      AppCenter has been available since 20.03, but it is of little use. This is because there is no functioning PackageKit backend for Nix 2.0. The Flatpak backend will not work before <link xlink:href="https://github.com/elementary/appcenter/issues/1076">flag for Flatpak-only</link> is provided. See this <link xlink:href="https://github.com/NixOS/nixpkgs/issues/70214">issue</link>.
      </para>
      <para>
       To use AppCenter on NixOS, add <literal>pantheon.appcenter</literal> to <xref linkend="opt-environment.systemPackages" />, <link linkend="module-services-flatpak">enable Flatpak support</link> and optionally add the <literal>appcenter</literal> Flatpak remote: