Add note on docker service update --mode

docs/index.html

@@ -2132,6 +2132,22 @@ Note: if the hash rate goes to zero and doesn't climb back up, try to `rm` and `
 
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+## Why do we have to re-create the service to enable global scheduling?
+
+- Enabling it dynamically would make rolling updates semantics very complex
+
+- This might change in the future (after all, it was possible in 1.12 RC!)
+
+- As of Docker Engine 1.13, other parameters requiring to `rm`/`create` the service are:
+
+  - service name
+
+  - hostname
+
+  - network
+
+---
+
 ## Checkpoint
 
 - We've seen how to set up a Swarm
@@ -2325,8 +2341,6 @@ I don't need to SSH to another node.
 
 ]
 
-Note: we could also use a pre-built image, e.g. `nicolaka/netshoot`
-
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 ## Investigating the `rng` service