Merge branch 'en/ort-becomes-the-default'

Use `ort` instead of `recursive` as the default merge strategy.

* en/ort-becomes-the-default:
  Update docs for change of default merge backend
  Change default merge backend from recursive to ort

diff --cc Documentation/merge-options.txt
Simple merge

diff --cc builtin/merge.c
Simple merge

diff --cc builtin/rebase.c
Simple merge

diff --cc sequencer.c
Simple merge