Add build-debian to .gitignore
Add build-debian to .gitignore

Adds the /doc/install-guide-rst/build-debian/
build directory to .gitignore

Change-Id: Iaea99de92f33cd7423694c16c90d2fe01d4369b0

AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,saeki-masaki/openstack-manuals,Akasurde/openstack-manuals,openstack/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,potsmaster/openstack-manuals,openstack/openstack-manuals,kairoaraujo/openstack-manuals,potsmaster/openstack-manuals,openstack/openstack-manuals