Add a bit of description about how handles work in the C API.

include/cameraserver_c.h

@@ -17,6 +17,17 @@ extern "C" {
 
 struct CvMat;
 
+//
+// The C API is handle-based.  Sources and sinks are reference counted
+// internally to the library.  Any time a source or sink handle is returned
+// or provided to a callback, the reference count is incremented.
+// Calling CS_ReleaseSource() or CS_ReleaseSink() decrements the reference
+// count, and when the reference count reaches zero, the object is destroyed.
+// Connecting a source to a sink increments the reference count of the source,
+// and when the sink is destroyed (its reference count reaches zero), the
+// source reference count is decremented.
+//
+
 //
 // Typedefs
 //