.gitignore: refine for generated docs.
.gitignore: refine for generated docs.

gbeauchesne/gstreamer-vaapi,sreerenjb/sree-gstreamer-vaapi,CapOM/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,sreerenjb/sree-gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi,sreerenjb/sree-gstreamer-vaapi,gbeauchesne/gstreamer-vaapi,CapOM/gstreamer-vaapi,CapOM/gstreamer-vaapi,01org/iotg-lin-gfx-gstreamer-vaapi,GStreamer/gstreamer-vaapi,GStreamer/gstreamer-vaapi