RelNotes: spelling & grammar tweaks

Signed-off-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git 2.2

Signed-off-by: Junio C Hamano <gitster@pobox.com>
repack: warn when "-l" is not used with alternates

Failing to use "-l" means that we will copy objects from the
source repository, nullifying the usefulness of "-s". We
don't want to make this an error, though, since "git repack
-a" is used to intentionally break the dependency.