Update .gitignore

I store release tarballs in a subdirectory of my git repo, so I needed
an update to my .gitignore file

Signed-off-by: Doug Ledford <dledford@redhat.com>
diff --git a/.gitignore b/.gitignore
index d198dd1..9fb29ea 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,3 +21,4 @@
 config/ltsugar.m4
 config/ltversion.m4
 config/lt~obsolete.m4
+tarballs/