update readme

README.org

@@ -93,6 +93,7 @@
         }
       #+END_SRC
 
+      This trait is sealed, and we have it already implemented for all handle types, so you rarely need to use it yourself, unless you want a function that operates on any type of handle.
 **** Error handling
      There is provided an idiomatic Rust error handling module, with conversion and interop between the C ABI ~GHOST_TSuccess~ and the Rust ~error::GhostError~.
      There is also the type alias ~GhostResult~ provided.