bup-index.md: make it clear that *bup* doesn't expand --exclude paths.
bup-index.md: make it clear that *bup* doesn't expand --exclude paths.

Signed-off-by: Rob Browning <1dc5917c2adeeba13d1ef33dbb40691a1b67cc65@defaultvalue.org>

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