Document removal of LTS Haskell package sets in 16.09 release notes.

This patch closes #14897.

nixos/doc/manual/release-notes/rl-1609.xml

@@ -69,6 +69,25 @@ following incompatible changes:</para>
     </para>
   </listitem>
 
+  <listitem>
+    <para>Previous versions of Nixpkgs had support for all versions of the LTS
+    Haskell package set. That support has been dropped. The previously provided
+    <literal>haskell.packages.lts-x_y</literal> package sets still exist in
+    name to aviod breaking user code, but these package sets don't actually
+    contain the versions mandated by the corresponding LTS release. Instead,
+    our package set it loosely based on the latest available LTS release, i.e.
+    LTS 7.x at the time of this writing. New releases of NixOS and Nixpkgs will
+    drop those old names entirely. <link
+    xlink:href="http://lists.science.uu.nl/pipermail/nix-dev/2016-June/020585.html">The
+    motivation for this change</link> has been discussed at length on the
+    <literal>nix-dev</literal> mailing list and in <link
+    xlink:href="https://github.com/NixOS/nixpkgs/issues/14897">Github issue
+    #14897</link>. Development strategies for Haskell hackers who want to rely
+    on Nix and NixOS have been described in <link
+    xlink:href="http://lists.science.uu.nl/pipermail/nix-dev/2016-June/020642.html">another
+    nix-dev article</link>.</para>
+  </listitem>
+
   <listitem>
     <para>Shell aliases for systemd sub-commands
     <link xlink:href="https://github.com/NixOS/nixpkgs/pull/15598">were dropped</link>: