doc: add release notes for a wafHook change

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

@@ -57,6 +57,15 @@
           new versions will release.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          The <literal>wafHook</literal> hook now honors
+          <literal>NIX_BUILD_CORES</literal> when
+          <literal>enableParallelBuilding</literal> is not set
+          explicitly. Packages can restore the old behaviour by setting
+          <literal>enableParallelBuilding=false</literal>.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
   <section xml:id="sec-release-22.05-notable-changes">

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

@@ -10,7 +10,7 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 ## Backward Incompatibilities {#sec-release-22.05-incompatibilities}
 
-* `pkgs.ghc` now refers to `pkgs.targetPackages.haskellPackages.ghc`.
+- `pkgs.ghc` now refers to `pkgs.targetPackages.haskellPackages.ghc`.
   This *only* makes a difference if you are cross-compiling and will
   ensure that `pkgs.ghc` always runs on the host platform and compiles
   for the target platform (similar to `pkgs.gcc` for example).
@@ -22,9 +22,11 @@ In addition to numerous new and upgraded packages, this release has the followin
   instead to ensure cross compilation keeps working (or switch to
   `haskellPackages.callPackage`).
 
-* `pkgs.emacsPackages.orgPackages` is removed because org elpa is deprecated.
+- `pkgs.emacsPackages.orgPackages` is removed because org elpa is deprecated.
   The packages in the top level of `pkgs.emacsPackages`, such as org and
   org-contrib, refer to the ones in `pkgs.emacsPackages.elpaPackages` and
   `pkgs.emacsPackages.nongnuPackages` where the new versions will release.
 
+- The `wafHook` hook now honors `NIX_BUILD_CORES` when `enableParallelBuilding` is not set explicitly. Packages can restore the old behaviour by setting `enableParallelBuilding=false`.
+
 ## Other Notable Changes {#sec-release-22.05-notable-changes}