docs(README): Point out where to find nightly/master docs. #682

	name: Deploy Docs

	on:
	push:
	branches:
	- stable
	- master

	# Builds all docs for both stable and master branches.
	# In the gh-pages branch, we place:
	# stable user-guide at /
	# master user-guide at /devel
	# master dev-guide at /dev-guide

	jobs:
	doc:
	name: Documentation
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v4
	with:
	fetch-depth: 0
	- name: Install mdbook
	run: \|
	mkdir mdbook
	curl -Lf https://github.com/rust-lang/mdBook/releases/download/v0.4.37/mdbook-v0.4.37-x86_64-unknown-linux-gnu.tar.gz \| tar -xz --directory=./mdbook
	echo "`pwd`/mdbook" >> $GITHUB_PATH
	- name: Build book
	run: \|
	# Build for stable
	git checkout stable
	# Support both old and new directory structure during the transition
	cd doc/user-guide \|\| cd doc
	mdbook build
	mv book ${{ runner.temp }}
	# Build for master
	cd $(git rev-parse --show-toplevel)
	git checkout master
	cd doc/user-guide
	mdbook build
	mv book ${{ runner.temp }}/book/devel
	# Build dev-guide for master
	cd ../dev-guide
	mdbook build
	mv book ${{ runner.temp }}/book/dev-guide
	- name: Deploy to GitHub
	run: \|
	cd ${{ runner.temp }}/book
	git init
	git config user.name "Deploy from CI"
	git config user.email ""
	git add . .nojekyll
	git commit -m "Deploy $GITHUB_REF $GITHUB_SHA to gh-pages"
	git remote add origin https://x-access-token:${{ secrets.GITHUB_TOKEN }}@github.com/$GITHUB_REPOSITORY
	git push --force --set-upstream origin master:gh-pages

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