Prefer direnv's use_nix to shell.nix

I find it bothersome to share the list of Haskell dependencies between my
default.nix and shell.nix files. A few days ago, I created a THIRD file,
shared.nix, that defined the shared code b/w default.nix and shell.nix. This
DRY'd things up, but it also added a new file, which I didn't like.

Today I learned that direnv integrates with Nix using a function called
`use_nix`. Voila! I typically already have .envrc files per-project, so this
doesn't add any unnecessary files, and it allows me to delete my shell.nix
files.

I would use `lorri`, except that I encountered issues using Lorri on my work
computer, which I'm not interested in attempting to resolve now.

1 files changed, 1 insertions, 0 deletions

diff --git a/zoo/.envrc b/zoo/.envrc
new file mode 100644
index 000000000000..4a4726a5c73f
--- /dev/null
+++ b/zoo/.envrc
@@ -0,0 +1 @@
+use_nix