Update documentation about automatic issue closing

RE !1933 (merged)

mentioned in merge request !1933 (merged)

Added 46 commits:

• a426fb15...f5430e48 - 45 commits from branch master
• 048605bd - Merge branch 'master' into issue-closing-docs

Reassigned to @rspeicher

Status changed to merged

mentioned in commit 275e8e73

Mentioned in commit 842cf813

Mentioned in commit 79d94b16

Mentioned in commit 6e798d2a

Mentioned in commit 5614d724

mentioned in commit 2a51557b