Merge branch 'cleanup/handbook-parallel' into 'master'

Timo Kochrequested to merge
cherry-pick-0743f883 into releases/3.2

[cleanup][handbook] update parallel section with new linear solver

See merge request !2106 (merged)

(cherry picked from commit 0743f883)

82bc87e7 [cleanup][handbook] update parallel section with new linear solver

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