Improve error message for "setup.py upload" without dist files (GH-21060)

(cherry picked from commit 08a6926b2584040fe3c3f06263b0b5f1fbbdc24c)

Co-authored-by: Éric Araujo <merwok@netwok.org>
diff --git a/Lib/distutils/command/upload.py b/Lib/distutils/command/upload.py
index f7752f9..32dda35 100644
--- a/Lib/distutils/command/upload.py
+++ b/Lib/distutils/command/upload.py
@@ -57,7 +57,8 @@
 
     def run(self):
         if not self.distribution.dist_files:
-            msg = "No dist file created in earlier command"
+            msg = ("Must create and upload files in one command "
+                   "(e.g. setup.py sdist upload)")
             raise DistutilsOptionError(msg)
         for command, pyversion, filename in self.distribution.dist_files:
             self.upload_file(command, pyversion, filename)