Document order option in update_config (#5089)

compose/compose-file/compose-versioning.md

@@ -264,6 +264,7 @@ Introduces the following additional parameters:
 - `order` for [update configurations](index.md#update_config)
 - `name` for [volumes](index.md#volume-configuration-reference)
 
+
 ## Upgrading
 
 ### Version 2.x to 3.x

compose/compose-file/index.md

@@ -739,9 +739,13 @@ updates.
   (default: `pause`).
 - `monitor`: Duration after each task update to monitor for failure `(ns|us|ms|s|m|h)` (default 0s).
 - `max_failure_ratio`: Failure rate to tolerate during an update.
+- `order`: Order of operations during updates. One of `stop-first` (old task is stopped before starting new one), or `start-first` (new task is started first, and the running tasks will briefly overlap) (default `stop-first`) **Note**: Only supported for v3.4 and higher.
+
+> **Note**: `order` is only supported for v3.4 and higher of the compose
+file format.
 
 ```none
-version: '3'
+version: '3.4'
 services:
   vote:
     image: dockersamples/examplevotingapp_vote:before
@@ -752,6 +756,7 @@ services:
       update_config:
         parallelism: 2
         delay: 10s
+        order: stop-first
 ```
 
 #### Not supported for `docker stack deploy`