Update README.

Author: mbostock

README.md

@@ -14,6 +14,10 @@ In a vanilla environment, a `d3_timer` global is exported. [Try d3-timer in your
 
 ## API Reference
 
+<a name="now" href="#now">#</a> d3.<b>now</b>()
+
+Returns the current time as defined by [performance.now](https://developer.mozilla.org/en-US/docs/Web/API/Performance/now) if available, and [Date.now](https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Date/now) if not. The current time is updated at the start of a frame; it is thus consistent during the frame, and any timers scheduled during the same frame will be synchronized. If this method is called outside of a frame, such as in response to a user event, the current time is calculated and then fixed until the next frame, again ensuring consistent timing during event handling.
+
 <a name="timer" href="#timer">#</a> d3.<b>timer</b>(<i>callback</i>[, <i>delay</i>[, <i>time</i>]])
 
 Schedules a new timer, invoking the specified *callback* repeatedly until the timer is [stopped](#timer_stop). An optional numeric *delay* in milliseconds may be specified to invoke the given *callback* after a delay; if *delay* is not specified, it defaults to zero. The delay is relative to the specified *time* in milliseconds; if *time* is not specified, it defaults to [now](#now).
@@ -62,7 +66,3 @@ Like [timer](#timer), except the timer automatically [stops](#timer_stop) on its
 <a name="timerFlush" href="#timerFlush">#</a> d3.<b>timerFlush</b>()
 
 Immediately invoke any eligible timer callbacks. Note that zero-delay timers are normally first executed after one frame (~17ms). This can cause a brief flicker because the browser renders the page twice: once at the end of the first event loop, then again immediately on the first timer callback. By flushing the timer queue at the end of the first event loop, you can run any zero-delay timers immediately and avoid the flicker.
-
-<a name="now" href="#now">#</a> d3.<b>now</b>()
-
-Returns the current time as defined by [performance.now](https://developer.mozilla.org/en-US/docs/Web/API/Performance/now) if available, and [Date.now](https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/Date/now) if not. The current time is updated at the start of a frame; it is thus consistent during the frame, and any timers scheduled during the same frame will be synchronized. If this method is called outside of a frame, such as in response to a user event, the current time is calculated and then fixed until the next frame, again ensuring consistent timing during event handling.