Clarify --prefer-binary

Author: notatallshaw

src/pip/_internal/cli/cmdoptions.py

@@ -670,7 +670,10 @@ def prefer_binary() -> Option:
         dest="prefer_binary",
         action="store_true",
         default=False,
-        help="Prefer older binary packages over newer source packages.",
+        help=(
+            "Prefer binary packages over source packages, even if the "
+            "source packages are newer."
+        ),
     )