Merge branch 'rp/apply-intent-to-add-fix'

"git apply -N" should start from the current index and register only new files, but it instead started from an empty index, which has been corrected. * rp/apply-intent-to-add-fix: apply docs: clarify wording for --intent-to-add t4140: test apply --intent-to-add interactions apply: only write intents to add for new files apply: read in the index in --intent-to-add mode