Add comment indicating that backports.entry_points_selectable is only needed for older Pythons.

Author: jaraco

setup.cfg

@@ -41,6 +41,7 @@ project_urls =
 packages = find:
 install_requires =
     appdirs>=1.4.3,<2
+    # required for Python 3.5 and 2.7 compatibility (3381339d)
     backports.entry_points_selectable>=1.0.4
     distlib>=0.3.1,<1
     filelock>=3.0.0,<4