Add .gitignore file
Add .gitignore file

Add initial .gitignore file, copied from openstack-manuals and
removed lines that are not needed for this repository.

Change-Id: Ia8fce06f4d24d01534623b9caa9a32945fd0f92e

openstack/openstack-doc-tools,savinash47/openstack-doc-tools,openstack/openstack-doc-tools,savinash47/openstack-doc-tools,savinash47/openstack-doc-tools