docs: Update include directive for gstreamer-base components
docs: Update include directive for gstreamer-base components

Change to always include gst/libs/base.h in order to also
include base-prelude.h, but also because it's the right
thing for people to include anyway.

https://bugzilla.gnome.org/show_bug.cgi?id=797165

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer