Merge branch 'pm/am-in-body-header-doc-update'

Doc update. * pm/am-in-body-header-doc-update: am: document that Date: can appear as an in-body header

Junio C Hamano committed Jan 8, 2020 at 12:44 UTC 202f68b252d3d4bcd6d02c0c135dc64e35348679

No changes.