gh-76303: Improve -x option documentation

[RoryGlenn]

Expand the documentation for the -x command-line option to explain its purpose and usage for turning Python scripts into Windows batch files, with examples of batch file header lines.

The current documentation is a single line:

Skip the first line of the source, allowing use of non-Unix forms of #!cmd. This is intended for a DOS specific hack only.

This gives virtually no information about why the option exists or how to use it. As noted by @serhiy-storchaka in the issue, the purpose of -x is to allow turning Python scripts into Windows batch files (similar to how shebang lines work on Unix).

The expanded documentation now includes:

• A clear explanation of the use case (Windows batch files)
• Two practical examples of batch file header lines
• An explanation of why -x is needed (the header line is not valid Python syntax)

• Issue: Improve -x option documentation #76303

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📚 Documentation preview 📚: https://cpython-previews--144857.org.readthedocs.build/

[brianschubert]

News entries are not needed for docs changes - this can be deleted. See Changes that require NEWS entries for more on what changes do/do not require a new entry

[brianschubert]

Fix trailing whitespace lints (my bad!)

Suggested change

	.. code-block:: batch
	@py -x "%~f0" %* & exit /b
	Or, to specify the path to the Python interpreter explicitly:
	.. code-block:: batch
	@"C:\Path\to\python.exe" -x "%~f0" %* & exit /b
	.. code-block:: batch
	@py -x "%~f0" %* & exit /b
	Or, to specify the path to the Python interpreter explicitly:
	.. code-block:: batch
	@"C:\Path\to\python.exe" -x "%~f0" %* & exit /b