docs for new read-snip-from-port function in the wxme library

original commit: a4336c39976d10974e2e74151e8e7cfd36c92ee2

collects/scribblings/gui/wxme.scrbl

@@ -245,6 +245,16 @@ editor's content.
 The @racket[what] argument is as for @method[stream<%> read-integer].}
 }
 
+@defproc[(read-snip-from-port [name string?]
+                              [who any/c]
+                              [stream (is-a?/c stream<%>)])
+         bytes?]{
+  Given @racket[name], which is expected to be the name of a snipclass,
+  uses that snipclass to read from the given stream at the current point
+  in that stream. Returns the processed bytes, much like the
+  @method[snip-reader<%> read-snip] method.
+}
+
 @; ----------------------------------------------------------------------
 
 @section[#:tag "snipclassmapping"]{Snip Class Mapping}