Fixes #19 Updating README and adding an example for use-external-python#7

	on:
	push:
	pull_request:
	name:Check python installation
	jobs:
	pythoninstall:
	name:Test Python install
	runs-on:${{ matrix.os }}
	strategy:
	matrix:
	os:[ubuntu-latest]
	python-version:['3.11']
	use-external-python:[true, false]
	env:
	python-test-package:python-dummy
	steps:
	-uses:actions/checkout@v4

	-name:Install Python if required
	if:${{ matrix.use-external-python }}
	uses:actions/setup-python@v5
	with:
	python-version:${{ matrix.python-version }}

	-name:Install a test dependency if external Python is used
	if:${{ matrix.use-external-python }}
	run:
	pip install ${{ env.python-test-package }}

	-name:Test Action usage
	uses:./
	with:
	python-root-list:"./tests/.py ./tests/subtest/.py"
	use-black:true
	use-isort:true
	use-mypy:true
	use-pycodestyle:true
	use-pydocstyle:true
	extra-pycodestyle-options:"--max-line-length=88"
	use-pylint:false
	use-flake8:false
	use-vulture:true
	python-version:${{ matrix.python-version }}
	use-external-python:${{ matrix.use-external-python }}

	-name:Check if test dependency exists after execution
	run:\|
	pip freeze > all-deps.txt
	should_appear=$( if [[ "${{ matrix.use-external-python }}" == "true" ]]; then echo 0; else echo 1; fi )
	line_exists=$( grep -qF "${{ env.python-test-package }}" "all-deps.txt"; echo $? )
	echo "test package should be installed: ${{ matrix.use-external-python }}"
	echo "test package is present (0 = present): ${line_exists}"
	cat all-deps.txt
	test "${should_appear}" == "${line_exists}"

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