add Hoogle

The `hoogle` command is useful, among other things, for searching the
used libraries for functions, ie:

```console
hoogle 'a -> a'
GHC.Prelude id :: a -> a
..
```

You can also start a web-server:

```console
hoogle server
```

1 files changed, 1 insertions, 0 deletions

diff --git a/default.nix b/default.nix
index 4b4c392..2bb0824 100644
--- a/default.nix
+++ b/default.nix
@@ -30,6 +30,7 @@ rec {
       pkgs.ghcid
       pkgs.git
     ];
+    withHoogle = true;
     shellHook = ''
       HISTFILE=${pkgs.lib.escapeShellArg ./.}/.history; export HISTFILE
     '';