Clarify comment

Author: johnslavik

Lib/pdb.py

@@ -190,7 +190,8 @@ def __init__(self, target):
             print(f'Error: {target} is a directory')
             sys.exit(1)
 
-        # Be careful with realpath to support pseudofilesystems (GH-142315).
+        # Use the original path for files like anonymous pipes
+        # from process substitution (GH-142315).
         realpath = os.path.realpath(target)
         self._target = realpath if os.path.exists(realpath) else target