Initiate docs also on PRs #11

Job	Run time
Build (Debug)	4m 0s
Build (Release)	3m 35s
Build (RelWithDebInfo)	5m 6s
Build (RelWithDebInfo-noEigen)	4m 25s
Build & Test (RelWithDebInfo, no Eigen)	6m 2s
Build & Test (RelWithDebInfo + Eigen)	7m 6s
Build Docs	0s
	30m 14s

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