Spec: Clarify repository root

specification.md

@@ -544,7 +544,7 @@ This is the main compiler executable, sometimes referred to as *driver*.
 
 The following directory layout is used.
 
-    mcc/
+    mcc/                                    # This node represents the root of your repository.
     ├── app/                                # Each C file in this directory corresponds to one executable.
     │   ├── mc_ast_to_dot.c
     │   ├── mcc.c