Add the phrase declarative config for easier searching

docs/setuptools.txt

@@ -2305,7 +2305,7 @@ Configuring setup() using setup.cfg files
 
 ``Setuptools`` allows using configuration files (usually :file:`setup.cfg`)
 to define a package’s metadata and other options that are normally supplied
-to the ``setup()`` function.
+to the ``setup()`` function (declarative config).
 
 This approach not only allows automation scenarios but also reduces
 boilerplate code in some cases.