Fix the chrome.runtime.onInstalled docs to note it fires for updates as well.

chrome/common/extensions/api/runtime.json

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [
   {
     "namespace": "runtime",
     "documentation_permissions_required": ["runtime"],
     "properties": {
       "lastError": {
@@ skipping 94 matching lines @@
         "returns": {
           "type": "string",
           "description": "The fully-qualified URL to the resource."
         }
       }
     ],
     "events": [
       {
         "name": "onInstalled",
         "type": "function",
-        "description": "Fired when the extension is first installed."
+        "description": "Fired when the extension is first installed, and on each update to a new version."
       },
       {
         "name": "onSuspend",
         "type": "function",
         "description": "Sent to the event page just before it is unloaded. This gives the extension opportunity to do some clean up. Note that since the page is unloading, any asynchronous operations started while handling this event are not guaranteed to complete. If more activity for the event page occurs before it gets unloaded the onSuspendCanceled event will be sent and the page won't be unloaded. "
       },
       {
         "name": "onSuspendCanceled",
         "type": "function",
         "description": "Sent after onSuspend() to indicate that the app won't be unloaded after all."
       }
     ]
   }
 ]