Documentation: be precise about which date --pretty uses
Documentation: be precise about which date --pretty uses

This makes it explicit that the --pretty formats 'medium' and 'email' use the
author date (and ignore the committer date).

Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git