Update pep-0639.rst

Co-authored-by: Dominic Davis-Foster <dominic@davis-foster.co.uk>

Author: CAM-Gerlach

pep-0639.rst

@@ -389,7 +389,7 @@ and `deprecates <Deprecate license classifiers_>`_ the license classifiers
 in the ``Classifier`` field.
 
 The error and warning guidance in this section applies to build and
-publishing tools; user-facing install tools MAY be more lenient than
+publishing tools; end-user-facing install tools MAY be more lenient than
 mentioned here when encountering malformed metadata
 that does not conform to this specification.