release-notes: add info about disabled QML cache

nixos/doc/manual/from_md/release-notes/rl-2211.section.xml

@@ -937,6 +937,19 @@
           Add udev rules for the Teensy family of microcontrollers.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          The Qt QML disk cache is now disabled by default. This fixes a
+          long-standing issue where updating Qt/KDE apps would sometimes
+          cause them to crash or behave strangely without explanation.
+          Those concerned about the small (~10%) performance hit to
+          application startup can re-enable the cache (and expose
+          themselves to gremlins) by setting the envrionment variable
+          <literal>QML_FORCE_DISK_CACHE</literal> to
+          <literal>1</literal> using e.g. the
+          <literal>environment.sessionVariables</literal> NixOS option.
+        </para>
+      </listitem>
       <listitem>
         <para>
           systemd-oomd is enabled by default. Depending on which systemd

nixos/doc/manual/release-notes/rl-2211.section.md

@@ -298,6 +298,14 @@ Available as [services.patroni](options.html#opt-services.patroni.enable).
 
 - Add udev rules for the Teensy family of microcontrollers.
 
+- The Qt QML disk cache is now disabled by default. This fixes a 
+  long-standing issue where updating Qt/KDE apps would sometimes cause 
+  them to crash or behave strangely without explanation. Those concerned 
+  about the small (~10%) performance hit to application startup can 
+  re-enable the cache (and expose themselves to gremlins) by setting the 
+  envrionment variable `QML_FORCE_DISK_CACHE` to `1` using e.g. the 
+  `environment.sessionVariables` NixOS option.
+
 - systemd-oomd is enabled by default. Depending on which systemd units have
   `ManagedOOMSwap=kill` or `ManagedOOMMemoryPressure=kill`, systemd-oomd will
   SIGKILL all the processes under the appropriate descendant cgroups when the