enhance customization example

Author: RonnyPfannschmidt

README.rst

@@ -285,12 +285,21 @@ The callable must return the configuration.
 
 .. code:: python
 
+    # content of setup.py
+    import setuptools
+    
     def myversion():
         from setuptools_scm.version import get_local_dirty_tag
         def clean_scheme(version):
             return get_local_dirty_tag(version) if version.dirty else '+clean'
 
         return {'local_scheme': clean_scheme}
+    
+    setup(
+        ...,
+        use_scm_version=myversion,
+        ...
+    )
 
 
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