pwg: improve negotiation documentation some more
pwg: improve negotiation documentation some more

lubosz/gstreamer,krichter722/gstreamer,cfoch/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,ensonic/gstreamer,jpakkane/gstreamer,ensonic/gstreamer,lovebug356/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,surround-io/gstreamer,jpxiong/gstreamer,jpakkane/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,mparis/gstreamer,Lachann/gstreamer,StreamUtils/gstreamer,Lachann/gstreamer,cfoch/gstreamer,justinjoy/gstreamer,lovebug356/gstreamer,surround-io/gstreamer,lubosz/gstreamer,collects/gstreamer,StreamUtils/gstreamer,cablelabs/gstreamer,krieger-od/gstreamer,StreamUtils/gstreamer,lubosz/gstreamer,centricular/gstreamer,krieger-od/gstreamer,ensonic/gstreamer,surround-io/gstreamer,Lachann/gstreamer,centricular/gstreamer,collects/gstreamer,mparis/gstreamer,jpxiong/gstreamer,ensonic/gstreamer,lubosz/gstreamer,ensonic/gstreamer,centricular/gstreamer,Lachann/gstreamer,justinjoy/gstreamer,mparis/gstreamer,cfoch/gstreamer,cablelabs/gstreamer,krichter722/gstreamer,collects/gstreamer,StreamUtils/gstreamer,centricular/gstreamer,justinjoy/gstreamer,cablelabs/gstreamer,lovebug356/gstreamer,cablelabs/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,krieger-od/gstreamer,jpakkane/gstreamer,krieger-od/gstreamer,krichter722/gstreamer,collects/gstreamer,justinjoy/gstreamer,jpakkane/gstreamer,jpxiong/gstreamer,lovebug356/gstreamer,krieger-od/gstreamer,lovebug356/gstreamer,jpxiong/gstreamer,collects/gstreamer,mparis/gstreamer,cfoch/gstreamer,Lachann/gstreamer,lubosz/gstreamer,shelsonjava/gstreamer,jpakkane/gstreamer,justinjoy/gstreamer,surround-io/gstreamer,cfoch/gstreamer,surround-io/gstreamer,StreamUtils/gstreamer,cablelabs/gstreamer