Small documentation improvements

* doc/org.texi (The Export Dispatcher): Reformulation.
* lisp/ox.el (org-export-copy-to-kill-ring): Comply to docstrings
  standards.

doc/org.texi

@@ -10408,10 +10408,10 @@ export dispatcher with the following key combinations:
 Toggle asynchronous export.  Asynchronous export uses an external Emacs
 process that is configured with a specified initialization file.
 
-While exporting asynchronously, the output is not displayed.  It is stored in
-a list called ``the export stack'', and can be viewed from there.  The stack
-can be reached by calling the dispatcher with a double @kbd{C-u} prefix
-argument, or with @kbd{&} key from the dispatcher.
+While exporting asynchronously, the output is not displayed, but stored in
+a place called ``the export stack''.  This stack can be displayed by calling
+the dispatcher with a double @kbd{C-u} prefix argument, or with @kbd{&} key
+from the dispatcher menu.
 
 @vindex org-export-in-background
 To make this behavior the default, customize the variable

lisp/ox.el

@@ -795,7 +795,8 @@ HTML code while every other back-end will ignore it."
   :type 'coding-system)
 
 (defcustom org-export-copy-to-kill-ring 'if-interactive
-  "Should we push exported content to the kill ring?"
+  "Non-nil means pushing export output to the kill ring.
+This variable is ignored during asynchronous export."
   :group 'org-export-general
   :version "24.3"
   :type '(choice