Update the packaging tutorial according to PEP 639

Author: befeleme

source/tutorials/packaging-projects.rst

@@ -213,9 +213,10 @@ following this tutorial.
     requires-python = ">=3.8"
     classifiers = [
         "Programming Language :: Python :: 3",
-        "License :: OSI Approved :: MIT License",
         "Operating System :: OS Independent",
     ]
+    license = "MIT"
+    license-files = ["LICEN[CS]E*"]
 
     [project.urls]
     Homepage = "https://github.com/pypa/sampleproject"
@@ -242,11 +243,15 @@ following this tutorial.
   packages until it finds one that has a matching Python version.
 - ``classifiers`` gives the index and :ref:`pip` some additional metadata
   about your package. In this case, the package is only compatible with Python
-  3, is licensed under the MIT license, and is OS-independent. You should
-  always include at least which version(s) of Python your package works on,
-  which license your package is available under, and which operating systems
+  3 and is OS-independent. You should
+  always include at least which version(s) of Python your package works on
+  and which operating systems
   your package will work on. For a complete list of classifiers, see
   https://pypi.org/classifiers/.
+- ``license`` is the :term:`SPDX license expression <License Expression>` of
+  your package.
+- ``license-files`` is the list of glob paths to the license files,
+  relative to the directory where :file:`pyproject.toml` is located.
 - ``urls`` lets you list any number of extra links to show on PyPI.
   Generally this could be to the source, documentation, issue trackers, etc.
 
@@ -305,6 +310,9 @@ MIT license:
 
 Most build backends automatically include license files in packages. See your
 backend's documentation for more details.
+If you include the path to license in the ``license-files`` key of
+:file:`pyproject.toml`, and your build backend supports :pep:`639`,
+the file will be automatically included in the package.
 
 
 Including other files