Documentation/bup-save.md: document --date option.
Documentation/bup-save.md: document --date option.

Signed-off-by: Jakob Matthes <57b4a576fb7c97f72cfdcdcd3fcd09d1a25e4cdb@gmail.com>
Reviewed-by: Rob Browning <1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org>

tjanez/bup,apenwarr/bup,pombredanne/bup,tjanez/bup,mhoeher/bup,jbaber/bup,pombredanne/bup,mhoeher/bup,jbaber/bup,mhoeher/bup,mhoeher/bup,pombredanne/bup,mhoeher/bup,apenwarr/bup,pombredanne/bup,apenwarr/bup,ToxicFrog/bup,tjanez/bup,jbaber/bup,gevaerts/bup,ToxicFrog/bup,ToxicFrog/bup,gevaerts/bup,pombredanne/bup,pombredanne/bup,tjanez/bup,jbaber/bup,gevaerts/bup,gevaerts/bup,gevaerts/bup,tjanez/bup,mhoeher/bup,apenwarr/bup,ToxicFrog/bup,jbaber/bup,ToxicFrog/bup,tjanez/bup,jbaber/bup