add configuration of gbp

debian/gbp.conf

+[DEFAULT]
+debian-branch = debian/stretch
+upstream-branch = upstream/stretch
+debian-tag = debian/stretch/%(version)s
+upstream-tag = upstream/stretch/%(version)s
+
+[buildpackage]
+git-debian-branch = debian/stretch
+git-debian-tag = debian/stretch/%(version)s
+git-upstream-tag = upstream/stretch/%(version)s
+
+[import-orig]
+pristine-tar = True