add nightly status badge to README #1009

	# SPDX-FileCopyrightText: Contributors to the Power Grid Model project <powergridmodel@lfenergy.org>
	#
	# SPDX-License-Identifier: MPL-2.0


	name: Check Blocking Labels

	on:
	# run pipeline on pull request
	pull_request:
	types:
	- opened
	- synchronize
	- labeled
	- unlabeled
	# run pipeline on merge queue
	merge_group:
	# run this workflow manually from the Actions tab
	workflow_dispatch:

	concurrency:
	group: ${{ github.workflow }}-${{ github.ref }}-blocking-labels
	cancel-in-progress: true

	jobs:
	check-blocking-labels:
	runs-on: ubuntu-latest
	steps:

	- name: do-not-merge
	if: contains(github.event.pull_request.labels.*.name, 'do-not-merge')
	run: \|
	echo "This pull request should not be merged (do-not-merge)"
	exit 1

	- name: merge-target-first
	if: contains(github.event.pull_request.labels.*.name, 'merge-target-first')
	run: \|
	echo "The target branch of this PR should be merged first (merge-target-first)"
	exit 2

	- name: needs-unit-tests
	if: contains(github.event.pull_request.labels.*.name, 'needs-unit-tests')
	run: \|
	echo "This pull request needs (more) unit tests before it may be merged (needs-unit-tests)"
	exit 3

Provide feedback