webrtc: Minor documentation enhancement

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1194>

net/webrtc/src/lib.rs

@@ -4,6 +4,8 @@
 /**
  * plugin-rswebrtc:
  *
+ * This plugin implements a high level WebRTC sink and source.
+ *
  * Since: plugins-rs-0.9
  */
 use gst::glib;

net/webrtc/src/webrtcsink/mod.rs

@@ -4,7 +4,7 @@ use crate::signaller::Signallable;
 /**
  * element-webrtcsink:
  *
- * {{ net/webrtc/README.md[0:190] }}
+ * {{ net/webrtc/README.md[2:190] }}
  *
  */
 use gst::glib;