gh-123345: improve fnmatch docs

[picnixz]

• Issue: Improve the documentation of fnmatch #123345

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📚 Documentation preview 📚: https://cpython-previews--123346.org.readthedocs.build/

[barneygale]

LGTM!

[picnixz]

Friendly ping in case you forgot to hit "merge" @barneygale

[miss-islington-app]

Thanks @picnixz for the PR 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[miss-islington-app]

Thanks @picnixz for the PR 🌮🎉.. I'm working now to backport this PR to: 3.13.
🐍🍒⛏🤖

[bedevere-app]

GH-128775 is a backport of this pull request to the 3.12 branch.

[bedevere-app]

GH-128776 is a backport of this pull request to the 3.13 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot ARM64 MacOS M1 Refleaks NoGIL 3.13 has failed when building commit 05bd6cb.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1396/builds/794) and take a look at the build logs.
4. Check if the failure is related to this commit (05bd6cb) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1396/builds/794

Failed tests:

• test.test_concurrent_futures.test_thread_pool

Failed subtests:

• test_free_reference - test.test_concurrent_futures.test_thread_pool.ThreadPoolExecutorTest.test_free_reference

Summary of the results of the build (if available):

==

Click to see traceback logs

Traceback (most recent call last):
  File "/Users/ec2-user/buildbot/buildarea/3.13.itamaro-macos-arm64-aws.macos-with-brew.refleak.nogil/build/Lib/test/test_concurrent_futures/executor.py", line 131, in test_free_reference
    self.assertIsNone(wr())
    ~~~~~~~~~~~~~~~~~^^^^^^
AssertionError: <test.test_concurrent_futures.executor.MyObject object at 0x20002070090> is not None


Traceback (most recent call last):
  File "/Users/ec2-user/buildbot/buildarea/3.13.itamaro-macos-arm64-aws.macos-with-brew.refleak.nogil/build/Lib/test/test_concurrent_futures/executor.py", line 131, in test_free_reference
    self.assertIsNone(wr())
    ~~~~~~~~~~~~~~~~~^^^^^^
AssertionError: <test.test_concurrent_futures.executor.MyObject object at 0x20004070090> is not None