Update Changes.org and org.texi to reflect changes in org-timer.el

Update org.texi with a new section: Countdown timer.
Update ORGWEBPAGE/Changes.org with a section about timer/clock.
Also fix a small typo in a org-timer.el.

ORGWEBPAGE/Changes.org

@@ -255,6 +255,11 @@ possible with org-wikinodes.el, which is available in the contrib
 directory.  We also have some [[http://orgmode.org/worg/org-contrib/org-wikinodes.php][documentation]] for this feature up
 on Worg.
 
+*** Timer/clock enhancements
+
+=org-timer-set-timer= displays a countdow timer in the modeline.
+From the agenda, `J' invokes =org-agenda-clock-goto=.
+
 * Version 7.01
 :PROPERTIES:
 :CUSTOM_ID: v7.01

doc/org.texi

@@ -5874,7 +5874,7 @@ with the @kbd{/} key in the agenda (@pxref{Agenda commands}).  If you have
 these estimates defined consistently, two or three key presses will narrow
 down the list to stuff that fits into an available time slot.
 
-@node Relative timer,  , Effort estimates, Dates and Times
+@node Relative timer, Countdown timer, Effort estimates, Dates and Times
 @section Taking notes with a relative timer
 @cindex relative timer
 
@@ -5916,6 +5916,20 @@ by a certain amount.  This can be used to fix timer strings if the timer was
 not started at exactly the right moment.
 @end table
 
+@node Countdown timer,  , Relative timer, Dates and Times
+@section Countdown timer
+@cindex Countdown timer
+@kindex C-c C-x ;
+@kindex ;
+
+Calling @code{org-timer-set-timer} from an Org-mode buffer runs a countdown
+timer.  Use @key{;} from agenda buffers, @key{C-c C-x ;} everwhere else.
+
+@code{org-timer-set-timer} prompts the user for a duration and displays a
+countdown timer in the modeline.  @code{org-timer-default-timer} sets the
+default countdown value.  Giving a prefix numeric argument overrides this
+default value.
+
 @node Capture - Refile - Archive, Agenda Views, Dates and Times, Top
 @chapter Capture - Refile - Archive
 @cindex capture

lisp/org-timer.el

@@ -328,7 +328,7 @@ VALUE can be `on', `off', or `pause'."
 
 If `org-timer-default-timer' is not zero, suggest this value as
 the default duration for the timer.  If a timer is already set,
-prompt the use if she wants to replace it.
+prompt the user if she wants to replace it.
 
 Called with a numeric prefix argument, use this numeric value as
 the duration of the timer.