Create SECURITY.md #899

	# This action requires that any PR targeting the master branch should touch at
	# least one CHANGELOG file. If a CHANGELOG entry is not required, add the "Skip
	# Changelog" label to disable this action.

	name: changelog

	on:
	pull_request:
	types: [opened, synchronize, reopened, labeled, unlabeled]
	branches:
	- master

	jobs:
	changelog:
	runs-on: ubuntu-latest
	if: "!contains(github.event.pull_request.labels.*.name, 'Skip Changelog')"

	steps:
	- uses: actions/checkout@v2

	- name: Check for CHANGELOG changes
	run: \|
	# Only the latest commit of the feature branch is available
	# automatically (see https://github.com/webcomponents/polyfills). To
	# diff with the base branch, we need to fetch that too (and we only
	# need its latest commit).
	git fetch origin ${{ github.base_ref }} --depth=1
	if [[ $(git diff --name-only FETCH_HEAD \| grep CHANGELOG) ]]
	then
	echo "A CHANGELOG was modified. Looks good!"
	else
	echo "No CHANGELOG was modified."
	echo "Please add a CHANGELOG entry, or add the \"Skip Changelog\" label if not required."
	false
	fi

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