desktop: Additional note on open_object()'s behavior

src/desktop_util.hpp

@@ -37,6 +37,16 @@ namespace desktop {
  * If the content pointed to by @a path_or_url cannot be trusted, you should
  * either refrain from using this function, or warn the user before calling
  * this function.
+ *
+ * @note Currently, only X11, Apple OS X, and Microsoft Windows are supported.
+ *       Using this function on unsupported platforms will result in an error
+ *       message logged in stderr.
+ *
+ * @return @a true on success, @a false otherwise. Failure to perform the
+ *         platform call means either that we do not currently support the
+ *         running platform, the child process exited with a non-zero status,
+ *         or something else went wrong. Thus, a value of @a true does not
+ *         truly guarantee success -- take it with a grain of salt.
  */
 bool open_object(const std::string& path_or_url);