Improve the realse notes with the upcoming documentation links, and a better example of how to convert overridePackages usage.

nixos/doc/manual/release-notes/rl-1703.xml

@@ -11,9 +11,9 @@ has the following highlights: </para>
 
 <itemizedlist>
   <listitem>
-    <para>Nixpkgs is now extensible through <link
+    <para>Nixpkgs is now extensible through overlays. See the <link
-    xlink:href="https://github.com/NixOS/nixpkgs/pull/21243">overlays</link>.
+    xlink:href="https://nixos.org/nixpkgs/manual/#sec-overlays-install">Nixpkgs
-    See the Nixpkgs manual for more information.</para>
+    manual</link> for more information.</para>
   </listitem>
 </itemizedlist>
 
@@ -100,9 +100,29 @@ following incompatible changes:</para>
   </listitem>
 
   <listitem>
-    <para><literal>pkgs.overridePackages</literal> function no longer exists.
+
-     Instead import Nixpkgs a second time using <literal>import pkgs.path {
+    <para><literal>overridePackages</literal> function no longer exists.
-    overlays = [ <replaceable>...</replaceable> ]; }</literal>.</para>
+    It is replaced by <link
+    xlink:href="https://nixos.org/nixpkgs/manual/#sec-overlays-install">
+    overlays</link>.  For example, the following code:
+
+<programlisting>
+  let
+    pkgs = import &lt;nixpkgs&gt {};
+  in
+    pkgs.overridePackages (self: super: ...)
+</programlisting>
+
+    Should be replaced by:
+
+<programlisting>
+  let
+    pkgs = import &lt;nixpkgs&gt {}; in
+  in
+    import pkgs.path { overlays = [(self: super: ...)] }
+</programlisting>
+
+    </para>
   </listitem>
 </itemizedlist>