docs: fix packaging.licenses suggestion (#215)

* docs: fix packaging.licenses suggestion

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

README.md

@@ -38,11 +38,13 @@ print(str(pkg_info))  # core metadata
 If `project.license` is a string or `project.license-files` is present, then
 METADATA 2.4+ will be used. A user is expected to validate and normalize
 `metadata.license` with an SPDX validation tool, such as the one being added to
-`packaging`. Add something like this:
+`packaging`. Add something like this (requires packaging 24.2+):
 
 ```python
 if isinstance(metadata.license, str):
-    metadata.license = packaging.licenses.normalize_license_expression(metadata.license)
+    metadata.license = packaging.licenses.canonicalize_license_expression(
+        metadata.license
+    )
 ```
 
 A backend is also expected to copy entries from `project.licence_files`, which