Change in coreboot[master]: util/docker: Add docker container that builds the sphinx documentation

[Jonathan Neuschäfer (Code Review)]

Jonathan Neuschäfer has posted comments on this change. ( https://review.coreboot.org/25869 )

Change subject: util/docker: Add docker container that builds the sphinx documentation
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Patch Set 1: Code-Review+1

Thanks!

Zaolin had the idea to use netlify for this, but netlify apparently has problems with relative submodule URLs, so it would in its current state fail to clone coreboot.git.