Update docstring to reflect non-equal specifier preference

Co-authored-by: Paul Moore <p.f.moore@gmail.com>

src/pip/_internal/resolution/resolvelib/provider.py

@@ -65,6 +65,7 @@ def get_preference(
 
         * Prefer if any of the known requirements points to an explicit URL.
         * If equal, prefer if any requirements contain `===` and `==`.
+        * If equal, prefer if requirements include version constraints (e.g., `>=` or `<`).
         * If equal, prefer user-specified (non-transitive) requirements.
         * If equal, order alphabetically for consistency (helps debuggability).
         """