new bullet about event_register() and event_unregister()

Author: cpsievert

NEWS.md

@@ -6,7 +6,8 @@
 * The `orca()` function gains new arguments `more_args` and `...` for finer control over the underlying system commands.
 * Improved `event_data()` interface:
   * The `event` argument of the `event_data()` function now supports the following events: `plotly_selecting`, `plotly_brushed`, `plotly_brushing`, `plotly_restyle`, `plotly_legendclick`, `plotly_legenddoubleclick`, `plotly_clickannotation`, `plotly_afterplot`, `plotly_doubleclick`, `plotly_deselect`, `plotly_unhover`. 
-  * A new `priority` argument. By setting `priority='event'`, the `event` is treated like a true event: any reactive expression using the `event` becomes invalidated (regardless of whether the input values has changed). For an example, see `plotly_example("shiny", "event_priority")`
+    * New `event_register()` and `event_unregister()` functions for declaring which events to transmit over the wire (i.e., from the browser to the shiny server). Events that are likely to have large overhead are not registered by default, so you'll need to register these: `plotly_selecting`, `plotly_unhover`, `plotly_restyle`, `plotly_legendclick`, and `plotly_legenddoubleclick`.
+  * A new `priority` argument. By setting `priority='event'`, the `event` is treated like a true event: any reactive expression using the `event` becomes invalidated (regardless of whether the input values has changed). For an example, see `plotly_example("shiny", "event_priority")`.
 * The `method` argument of `plotlyProxyInvoke()` gains support for a `"reconfig"` method. This makes it possible to change just the configuration of a plot. For an example use, see `plotly_example("shiny", "event_data_annotation")`.
 
 ## IMPROVEMENTS