docs: Add "How to Set Up React User Authentication" Post #790

	name: File checks

	on:
	pull_request:
	branches: [ master ]

	jobs:
	yarn_lock_check:
	runs-on: ubuntu-latest
	steps:
	- name: Checkout code
	uses: actions/checkout@v2
	- name: Check if yarn.lock exists
	run: \|
	if [ -f yarn.lock ]
	then
	echo "yarn.lock exists."
	exit 1
	fi

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