add note to readme.md that right now this gem is part of ddtrace and not to be used on its own #68

	name: Check
	on:
	push:
	branches: [ main ]
	pull_request:
	# The branches below must be a subset of the branches above
	branches: [ main ]
	jobs:
	check:
	name: Check types
	runs-on: ubuntu-22.04
	steps:
	- uses: actions/checkout@v3
	- uses: ruby/setup-ruby@31a7f6d628878b80bc63375a93ae079ec50a1601 # v1.143.0
	with:
	ruby-version: '3.2'
	bundler-cache: true # runs 'bundle install' and caches installed gems automatically
	- name: Check for stale signature files
	run: bundle exec rake rbs:stale
	- name: Check for missing signature files
	run: bundle exec rake rbs:missing
	- name: Check types
	run: bundle exec rake steep:check
	- name: Record stats
	run: bundle exec rake steep:stats[md] >> $GITHUB_STEP_SUMMARY

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