xmonad-wrapper: link man pages instead of copying

pkgs/applications/window-managers/xmonad/wrapper.nix

···
 
   buildCommand = ''
     mkdir -p $out/bin $out/share
-    cp -r ${xmonadEnv}/share/man $out/share/man
+    ln -s ${xmonadEnv}/share/man $out/share/man
     makeWrapper ${xmonadEnv}/bin/xmonad $out/bin/xmonad \
       --set NIX_GHC "${xmonadEnv}/bin/ghc" \
       --set XMONAD_XMESSAGE "${xmessage}/bin/xmessage"