Use a real repo URL in the example setup.py references (pypa#533)

Sending folks that follow the example link to the sample project repo is
likely to be less confusing than sending them to GitHub's 404 page

Author: aritro01

source/tutorials/packaging-projects.rst

@@ -81,7 +81,7 @@ the values if you want:
         description="A small example package",
         long_description=long_description,
         long_description_content_type="text/markdown",
-        url="https://github.com/pypa/example-project",
+        url="https://github.com/pypa/sampleproject",
         packages=setuptools.find_packages(),
         classifiers=(
             "Programming Language :: Python :: 3",