Add a nix flake to have a devshell
diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000..e31c306
--- /dev/null
+++ b/.envrc
@@ -0,0 +1,4 @@
+if ! has nix_direnv_version || ! nix_direnv_version 2.2.1; then
+    source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/2.2.1/direnvrc" "sha256-zelF0vLbEl5uaqrfIzbgNzJWGmLzCmYAkInj/LNxvKs="
+fi
+use flake