Added CONTRIBUTING.md #130

	# https://github.com/peaceiris/actions-gh-pages

	name: build-docs

	on:
	push:
	branches:
	- main

	jobs:
	build:
	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v2

	- name: Update apt repositories
	run: sudo apt update

	- name: Install Doxygen & CMake & ninja
	run: \|
	sudo apt install doxygen cmake ninja-build
	doxygen --version
	cmake --version
	ninja --version

	- name: Build CMake build_docs target
	run: \| # this will generate a docs/html/** folder (configured in the Doxyfile)
	mkdir build && cd build
	cmake .. -GNinja -DBUILD_DOCS=ON
	ninja build_docs

	- name: Deploy generated documentation
	uses: peaceiris/actions-gh-pages@v3
	with:
	github_token: ${{ secrets.GITHUB_TOKEN }} # NOTE you must enable Read+write permissions in repository Settings -> Actions -> Workflow permissions -> toggle on Read and write permissions
	publish_branch: gh-pages
	publish_dir: ./docs/html # from
	destination_dir: . # deploy to a subdirectory: https://github.com/peaceiris/actions-gh-pages#%EF%B8%8F-deploy-to-subdirectory-destination_dir
	commit_message: docs - ${{ github.event.head_commit.message }}

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