DOC: initial sphinx and readthedocs stub #398

Job	Run time
publish-on-pypi	1m 45s
build-installer-on-windows / build	31m 23s
build-on-ubuntu / build	4m 25s
build-on-windows / build	27m 19s
build-on-macos / build	1s
publish-on-github	0s
	1h 4m 53s

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