Move emacs to top-level nix expression

When I run `nix-build -f '<briefcase>' -iA emacs`, readTree will define...
- pkgs
- depot
- briefcase
...and whatever else I choose to define.

1 files changed, 1 insertions, 0 deletions

diff --git a/default.nix b/default.nix
index 36dba2915b..dfc360ead5 100644
--- a/default.nix
+++ b/default.nix
@@ -8,6 +8,7 @@ let
   };
 in {
   nixos       = readTree ./nixos;
+  emacs       = readTree ./emacs;
   blog        = readTree ./blog;
   lisp        = readTree ./lisp;
   gopkgs      = readTree ./gopkgs;