Add more API doc details on service update version.

Hopefully this removes some confusion as to what this version number
should be.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
(cherry picked from commit 5bdfa19b8646839f9d704307aa6589c7d686db44)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Upstream-commit: 64b0c76151ceb7b26f9c7477f3044dac747d227b
Component: engine

components/engine/api/swagger.yaml

@@ -9345,7 +9345,10 @@ paths:
 
         - name: "version"
           in: "query"
-          description: "The version number of the service object being updated. This is required to avoid conflicting writes."
+          description: "The version number of the service object being updated.
+          This is required to avoid conflicting writes.
+          This version number should be the value as currently set on the service *before* the update.
+          You can find the current version by calling `GET /services/{id}`"
           required: true
           type: "integer"
         - name: "registryAuthFrom"