readDir: log with debug what path is being processed

src/libexpr/primops.cc

@@ -1990,6 +1990,7 @@ static RegisterPrimOp primop_readFileType({
 static void prim_readDir(EvalState & state, const PosIdx pos, Value * * args, Value & v)
 {
     auto path = realisePath(state, pos, *args[0]);
+    printTalkative("devenv readDir: '%1%'", path);
 
     // Retrieve directory entries for all nodes in a directory.
     // This is similar to `getFileType` but is optimized to reduce system calls