nixpkgs manual: move builders into one folder

+1 -1
doc/manual.xml
···
<xi:include href="builders/special.xml" />
<xi:include href="builders/images.xml" />
<xi:include href="languages-frameworks/index.xml" />
-
<xi:include href="packages/index.xml" />
+
<xi:include href="builders/packages/index.xml" />
</part>
<part>
<title>Contributing to Nixpkgs</title>
doc/packages/citrix.xml doc/builders/packages/citrix.xml
doc/packages/dlib.xml doc/builders/packages/dlib.xml
doc/packages/eclipse.xml doc/builders/packages/eclipse.xml
doc/packages/elm.xml doc/builders/packages/elm.xml
doc/packages/emacs.xml doc/builders/packages/emacs.xml
doc/packages/ibus.xml doc/builders/packages/ibus.xml
doc/packages/index.xml doc/builders/packages/index.xml
doc/packages/kakoune.xml doc/builders/packages/kakoune.xml
doc/packages/linux.xml doc/builders/packages/linux.xml
doc/packages/locales.xml doc/builders/packages/locales.xml
doc/packages/nginx.xml doc/builders/packages/nginx.xml
doc/packages/opengl.xml doc/builders/packages/opengl.xml
doc/packages/shell-helpers.xml doc/builders/packages/shell-helpers.xml
doc/packages/steam.xml doc/builders/packages/steam.xml
doc/packages/unfree.xml doc/builders/packages/unfree.xml
doc/packages/weechat.xml doc/builders/packages/weechat.xml
doc/packages/xorg.xml doc/builders/packages/xorg.xml