Move devshell to subdirectory

.envrc

@@ -1,3 +1,14 @@
+use_flake_extra_watch() {
+  watch_file devshell/*
+  for f in devshell/*; do
+    if [ "$f" -nt flake.nix ]; then
+      # nix-direnv doesn't check the dates on other files, so give it a kick via flake.nix
+      touch flake.nix
+    fi
+  done
+}
+
+use flake_extra_watch
 use flake
 
 # devshell needs the shellHook to run even when cached